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Welcome

Mission Statement 

The purpose of FLAPS-2-APPROACH is two-fold:  To document the construction of a Boeing 737 flight simulator, and to act as a platform to share aviation-related articles pertaining to the Boeing 737; thereby, providing a source of inspiration and reference to like-minded individuals.

I am not a professional journalist.  Writing for a cross section of readers from differing cultures and languages with varying degrees of technical ability, can at times be challenging. I hope there are not too many spelling and grammatical mistakes.

 

Note:   I have NO affiliation with ANY manufacturer or reseller.  All reviews and content are 'frank and fearless' - I tell it as I see it.  Do not complain if you do not like what you read.

I use the words 'modules & panels' and 'CDU & FMC' interchangeably.  The definition of the acronym 'OEM' is Original Equipment Manufacturer (aka real aicraft part).

 

All funds are used to offset the cost of server and website hosting (Thank You...)

No advertising on this website - EVER!

 

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If you see any errors or omissions, please contact me to correct the information. 

Journal Archive (Newest First)
Friday
Mar112016

BRT / DIM Functionality - Lights Test Switch

The annunciators in the Boeing 737 are very bright when illuminated, and the reason for the high intensity is justified - the designers want to ensure that any system warnings or cautions are quickly noted by a flight crew.

However, when flying at night for extended periods of time the bright lights can be tiring on your eyes.  Also, during critical flight phases such as during a night-time approach, the bright lights can become distracting.  At this time, the flight deck is usually dimmed in an attempt to conserve night vision. 

For example, the three green landing annunciators (Christmas tree lights), speed brake and flaps extension annunciators are all illuminated during the final segment of the approach.  At full intensity these annunciators can, at the very least, be distracting.

LEFT:  Lights Test switch.  The three way switch located on the Main Instrument Panel (MIP) Captain-side is used to toggle the intensity of connected annunciators.  The panel label reads TEST, BRT and DIM.  The switch in the photograph is an OEM switch which has been retrofitted to a Flight Deck Solutions (FDS) MIP.

To help minimize eye strain and to enable night vision to be maintained as much as possible, pilots can select from two light intensity levels to control the brightness output of the annunciators. 

Anatomy of the Lights Test Switch

The switch (a three-way toggle) which controls the light intensity (brightness level) is called the Lights Test switch.  The switch is located on the Main Instrument Panel (MIP).  The switch is not a momentary switch and whatever position the switch is left at it will stay at until toggled to another position.  The switch has three labelled positions: Lights Test, BRT and DIM. 

(i)           UP controls the lights test (labeled Lights Test);

(ii)          CENTRE is the normal position which enables the annunciators to illuminate at full intensity (labeled BRT); and,

(iii)         DOWN lowers the brightness level of the annunciators (labeled DIM).

OEM annunciators have a built-in Push-To-Test function, and each annunciator will illuminate when pushed.  The brightness level is pursuant to the position the Lights Test switch (DIM or BRT). 

The Lights Test will always illuminate all the annunciators at their full intensity (maximum brightness). An earlier article explains the Lights Test switch in more detail.

Special Conditions

When the Light Test switch is set to DIM, all the annunciators will be display at their minimum brightness.  The exception is the annunciators belonging to the Master Caution System (MCS), which are the master warning, fire bell and six packs, and the Autopilot Flight Director System (AFDS).  These annunciators will always illuminate at their full intensity because they are construed as primary caution and warning lights.

Variable Voltage

There is nothing magical about the design Boeing has used to allow DIM functionality; it is very simplistic.

Annunciators for the most part are powered by 28 volts; therefore, when the Lights Test switch is in the neutral position (center position labeled BRT) the bulbs are receiving 28 volts and will illuminate at full intensity.  Moving the switch to the DIM position reduces the voltage from 28 volts to 16.5 volts with a correspondingly lower output.  In the real aircraft, the DIM functionality (and Light Test) is controlled by a semi-mechanical system comprising relays and zener-type diodes that vary the voltage. 

Two Controlling Systems - your choice

The DIM and Lights Test functionality can be achieved in the simulator by using one of two systems - software or mechanical.

Software Controlled

The avionics suites developed by Prosim-AR, Project Magenta and Sim Avionics have the ability to conduct a full Lights Test in addition to allowing DIM functionality.  However, depending upon the hardware used, the individual Push-To-Test function of each annunciator may not be functional.  The DIM functionality is controlled directly by the avionics suite software; it is not a mechanical system as used in the real aircraft.

In ProSim737 the DIM function can be assigned to any switch from the configuration/switches and indicators menu.  In Sim Avionics the function is assigned and controlled by FSUPIC offsets within the IT interface software.

Mechanically Controlled

I have chosen to replicate the Lights Test and DIM functionality in a similar way to how it is done in the real aircraft. 

There are no benefits or advantages to either system – they are just different methods to achieve the same result.

Two Meanwell power supplies are used to provide the voltage required to illuminate the annunciators.  A 28 volt power supply enables the annunciators to be illuminated at their brightest intensity, while the less bright DIM functionality is powered by a 16.5 volt power supply (or whatever voltage you wish).

A heavy duty 20 amp 28 volt relay enables selection of either 28 volt or 16.5 volts.

DIM Board

A small board has been constructed from ABS plastic on which is mounted a 20 amp 28 volt relay and a terminal block. The board, called DIM is mounted behind and beneath the MIP. This facilitates easy access to the required power supplies mounted within the Power Supply Rack (PSR)

LEFT:  The DIM Board is surprisingly simple and comprises a single terminal block and a heavy duty 28 volt relay.  Wires are coloured and tagged to ensure that each wire is connected to the correct terminal (click to enlarge).

An important function of the DIM board is that it helps to minimise the number of wires required to connect the DIM functionality to the various annunciators and to the Lights Test switch.   

Interfacing and Connections

Prior to proceeding further, a very brief explanation is required to how the various panels receive power. 

Rather than connect several panels directly to a power supply, I have connected the power supplies to two 28 volt busbars - one busbar is located in the center pedestal and other is attached to the rear of the MIP.  The busbars act a centralised point from which power is distributed to any connected panels.  This allows the wiring to be more manageable, neater, and easily traceable if troubleshooting is required.

Likewise, there is a lights test busbar located in the center pedestal that provides a central area to connect any panel that is lights test compliant.  Without this busbar, any panel that was lights test compliant would require a separate wire to be connected to the Lights Test switch in the MIP.  To read more about this feature, navigate to the page that deals with the lights test busbar.

The below mud schematic may make it easier to understand.  To view the schematic at full size click the image.

A 28 volt busbar located in the center pedestal is used as a central point from which to connect various panels to (lower pale blue box).  

The busbar is connected to the terminal block located on the DIM board.  Wires from the terminal block then connect to a 16.5 and 28 volt power supply located in the PSR (orange boxes). 

The 28 volt relay is also wired directly to the terminal block on the DIM board and a single wire connects the relay with the Lights Test switch located in the MIP (green box). 

From the Lights Test switch, a single wire connects with the lights test busbar located in the center pedestal (pale blue box).  The purple box represents any panel that is Lights Test compliant - a single wire connects between a panel and the lights test busbar.

Although this appears very convoluted, the principle is comparatively simplistic.

How it Works

When the Lights Test switch is toggled to the DIM position the relay is closed.  This inhibits 28 volts from entering the circuit, but allowing 16.5 volts to reach the 28 volt busbar (located in the center pedestal); any annunciators connected to this busbar will now only receive 16.5 volts and the annunciators will glow at their lowest brightness level.  Conversely, when the switch is toggled  to BRT or to Lights Test, the relay opens and the busbar once again receives 28 volts.

Which Annunciators are Connected to DIM Functionality

The annunciators that connect with the DIM board are those in the fire suppression panel, various panels in the center pedestal, the forward and aft overhead, and in the MIP.  If further annunciators in other systems require dimming, then it is a matter of connecting the appropriate wires from the annunciator to the 28 volt busbar, and to the and lights test busbar, both of which are located in the center pedestal.

BELOW:  A rather haphazard video showing the two brightness levels.  The example shows the annunciators in the OEM Fire Suppression Panel (FSP).  The clicking sound in the background is the Lights Test switch being toggled from BRT to DIM and back again.  Note that the colour of the annunciator does not alter - only the intensity (brightness).  The colour change in the video, as the lights alter intensity, is caused by a colour temperature shift which is not visible to the naked eye but is recorded by the video.

Glossary

Annunciator - A light that illuminates under set conditions.  Often called a Korry.
Busbar - A bar that enables power to distributed to several items from a centralised point.
Mud Schematic - Australian colloquialism meaning a very simplistic diagram (often used in geological mapping / mud map).
Push-To-Test Function - All annunciators have the ability to be pushed inwards to test the circuit and to check if the globe/LED is operational.
OEM - Original Equipment Manufacturer aka real aircraft part.
Panel/Module - Used interchangeably and meaning an avionics panel that incorporates annunciators.
Toggled - A verb in English meaning to toggle, change or switch from one effect, feature, or state to another by using a toggle or switch.

Tuesday
Feb162016

Flight Testing The SimWorld MCP and EFIS

I use the Mode Control Panel (MCP) and Electronic Flight Instrument System (EFIS) produced by CP Flight.  These units have been the mainstay in the flight simulation community for several years and for the most part they are robust, reliable, and more or less look similar to the OEM units. 

Recently, other companies have begun to manufacture MCP and EFIS units to replicate the real aircraft part as closely as possible in both appearance and functionality. 

LEFT:  SimWorld MCP retrofitted into a Flight Deck Solutions (FDS) MIP.  Initial impressions exceed expectations, especially when comparing the appearance of the MCP to the OEM item.

SimWorld, located in Poland is a relatively new company that is making great leaps forward designing and manufacturing reproduction B737 panels and other parts.  One of SimWorld's premier items is their 'plug and play' MCP and EFIS.

I am currently in possession of a SimWorld MCP and two EFIS units.  These units have been retrofitted into a Flight Deck Solutions (FDS) MIP and flight testing has begun.  In due course a detailed review will be published.  I also will be, at the same time, reviewing the CANBUS system that SimWorld use to connect their various panels to the computer and Flight Simulator.

To test and evaluate the unit will take some time as the protocols I use are very thorough.  In the next few months (depending upon time) I should have enough data to enable a detailed review to be written.  The review will address at the minimum the following:

  • Manufacturing technique (materials, painting, lazer cutting, etc);
  • Accuracy and scale to the OEM MCP/EFIS
  • Robustness and longevity;
  • Functionality to OEM unit;
  • Quality assurance;
  • SimWorld pre-sales and after-sales support;
  • Reliability and consistency in operation; and,
  • An overview of the CANBUS system.

Note that I have no affiliation with SimWorld, or any other manufacturer.  This review will be a balanced opinion based on my use and the use and opinion of other users of the MCP and EFIS unit.

Glossary

EFIS - Electronic Flight Instrument System.
MCP - Mode Control Panel.
MIP - Main Instrument Panel.
OEM - Original Equipment Manufacturer (aka real aircraft parts).

Sunday
Jan312016

Replacement Curtains - B737 OEM Throttle Dust Curtains

Interesting items can arrive in the post.  Earlier today I opened a small parcel to find a collection of grey coloured pieces of material.  To anyone else they would appear exactly as they do – pieces of material stamped with numbers.

LEFT:  OEM dust covers for the Boeing throttle.

The throttle quadrant I use is original equipment manufacture (OEM) and once plied the skies above Europe.  As such it is a used item with the usual wear and tear you expect from a well-used aircraft part. 

One item that continually caught my attention was the dust curtains or skirts that sit behind the two thrust levers.  In my throttle, the curtains had been abused at some point and were torn and the edges looked rather ragged in appearance.  Although a replacement curtain could have been made by using vinyl or another similar material it would not be the same. 

The numbered pieces of material now have a home – they are OEM dust curtains that will replace the damaged curtains on the throttle.

Installing the Dust Curtains

The B737 throttle quadrant has three dust curtains.  Two on the outer side of the thrust levers and one double-sided curtain that resides between the thrust levers.  Each curtain comprises three parts sandwiched together and held by three screws. 

The parts are:

(i)     The thin aluminium arc which is the outer face plate;
(ii)    The actual curtain; and,
(iii)   The plastic arc retainer. 

The plastic arc retainer is curve-shaped and sits flush against the bare metal of the quadrant.  The dust curtain then lies above the retainer and beneath the outer face plate.

LEFT:  Dust curtains have been removed and the plastic retainer and aluminium arc can be seen along with one of the three attachment screws (click to enlarge).

Replacing the curtains is straightforward. Remove the three screws that hold the metal arc in place to the throttle, then gentle pry loose the aluminium strip beneath which are the dust curtain and plastic arc retainer.  It’s wise to ensure that you place the parts anatomically on the workbench as each of the items must be reassembled the same way it was removed.

One aspect of Boeing philosophy which makes building a flight simulator much easier is their reuse of parts from earlier airframes.  Boeing do not always redesign a part from scratch, but add to or change existing parts.  This philosophy can save the company millions of dollars.

For those who study this type of thing, you will know that dust curtains can come in differing colour shades.  In general, the older classic style throttle used a paler grey/cream coloured skirt whilst the Next Generation airframes use a standard light grey colour.  But, I would not get too concerned if the colour does not exactly match.

Why are the Dust Curtains Important

The main purpose of the dust curtainsis to minimise the chance of foreign bodies falling into the throttle mechanism.  Think pens, rubbers, straws, paper clips and coke can pull tabs (or anything else pilots play with in the flight deck).  The dust curtains are made from a fire retardant material (not asbestos) which minimises the chance of any fire/sparks from licking up the sides of the thrust levers in the unlikely event that a fire devlops inside the throttle quadrant.

For those keen to find replacement OEM dust curtains the stock numbers are: 69-33918-8 REF, 69-33918-9 REF-F and 69-33918-10 REF-F.

Glossary

Anatomically – Meaning items removed are placed on a table in the same position as they were when they were in place.
Curtain Arc – the semi circular arc that the dust curtains are attached to.
OEM – Original Equipment Manufacture (aka real aircraft part).
Plastic Arc Retainer – A piece of heavy duty plastic shaped as a curve (arc).

Tuesday
Jan192016

Protection for Interface Cards - USB Isolator

In the first of two previous posts we discussed surge protectors and the need for a protector to secure your simulator system from unwanted power surges.  The second post addressed circuit breakers in more detail and examined the different types of breakers that can be used.  In this final post I will discuss the use of an isolator to protect both your computer and any USB connected interface cards.

LEFT:  Phidget 3060 USB Isolator mounted on arcylic base (click to enlarge).

Multiple Phidget Card Failure

Recently I had to replace several Phidget interface cards.  The cards failed following failure of the internal power supply on my server computer.  The reason for the power supply failure is unknown, however for whatever reason a surge travelled through the USB port to the SMART module irreparably damaging two Phidget 0/16/16 cards and two Phidget 1066 motor controllers.

I contacted Phidgets in Canada who were very helpful in diagnosing the reason for the card failure.  Apparently it is not unheard of for powered Phidget cards to cease working following the failure of a computer power supply that Phidget cards are attached.

Potential Problem

The discussion with the technician highlighted a potential problem that Phidget cards are susceptible to.

When the internal computer power supply (CPS) fails the circuits are no longer fully operational which may cause unregulated power to briefly travel the shortest route to leave the system.  PCI cards and USB ports are for the most part totally unprotected and act as a first port of call for any unwanted transient power.  The power then travels through the connected USB cable to whatever is attached.  Although the surge (I will call it a surge) may only be a millisecond, it is enough to fatally damage or shorten the life of an attached interface card.  

Bear in mind that not every instance of a power supply failure will result in a surge; it depends on how the power supply failed.  In my case, when the power supply failed 5 volts continued to be distributed.  However, I believe the 5 volts was not clean power meaning that the voltage fluctuated.

The technician commented that it is relatively uncommon for the event described above to occur.  He suggested that a far more common issue is that, following the failure of a powered Phidget card, the unregulated power travels to the computer via the connected USB cable (the opposite direction to what happened in my situation).  In these circumstances, the USB port, PCI card, internal computer power supply, or worse still – the computer’s motherboard can be destroyed.

For a more detailed explanation with examples, I refer you to the Phidget website.

The Solution

Fortunately there is an easy solution to this potential problem – the Phidgets 3060 USB isolator.  

The isolator is connected between the USB port and the interface cards.  In this way the cards are protected from the computer and the computer is protected from the cards, wiring and external power supplies used to power the cards.

LEFT:  Phidget 3060 isolator – the size of a credit card, the isolator can provide protection for both the computer and the interface cards that are connected to it.  This isolator is installed into the SMART module and provides protection for the two 0/16/16 cards and two 1066 motor controllers (click to enlarge).

The 3060 isolator is a tad smaller than the standard-sized credit card and does not require a power supply.  The isolator has two USB connections, one side has a mini and the other side a standard connection.  This enables in-line connection of the isolator between the computer’s USB port and interface card/power hub.

LEFT:  The 3060 isolator installed into the Throttle Interface Module (TIM).  The isolator has been installed into an acrylic casing.  Although the casing is by no means necessary, it ensures that the isolator card does not become contaminated by dust.  The blue-coloured plastic band is temporary only (click to enlarge).

In addition to the protection already mentioned, the isolator also protects against possible basic wiring errors and different ground voltages.  In some circumstances the isolator can also assist to stabilise a system form untimely USB disconnects.  The isolator achieves this by maintaining the correct voltage.

The interface cards used in the simulator have been mounted in standalone interface modules that in turn connect via USB to the server computer.  To protect the contents of each module, a 3060 isolator has been installed into each interface module.

Computer Power Supplies (CPS)

Although this problem was easily solved by purchasing replacement interface cards and installing isolators, it should not have occurred in the first place and it brings into question the reliability and quality of computer power supplies.

The choice of a CPS is often by chance, being the unit supplied with the computer (probably a inexpensive Chinese model).  However, CPS’s are not identical and you get what you pay for.  

Many manufactures claim a specific output/voltage/wattage from their power supplies, however only a few manufactures check and guarantee these outputs.  The last thing you want is a power supply that has fluctuating voltage or a unit that is rated a particular output but does not meet this requirement.  

The CPS installed in the server computer was not a quality item (it came with the computer and was not upgraded despite the remainder of the computer being re-built to flight simulator specifications).  For a few months I had noted that the CPS appeared to be running quite warm.  In hindsight, I should have realized the tell-tail symptoms of an impending problem.  

The failed CPS has been replaced with a Corsair RM750x Power Supply.  This particular model is used when tight voltage control is needed.  

Other benefits of using a Corsair CPS is that the capacitors are Japanese made and provide consistent and reliable output.  Furthermore, Corsair bench check every unit to ensure that they meet the outputs published.

Final Call

It is your call whether the expenditure and use of a USB isolator is warranted.  Certainly replacing Phidget cards can be expensive, not too mention the time required to install and rewire.  The isolator should be viewed as a type of insurance policy  - a 'just in case' option.

Further Information

NOTE: The isolator is designed by Phidgets primarily to operate with powered Phidget cards.   The interface modules I use have Phidget, PoKeys and Leo Bodnar cards installed and connecting an isolator did not cause any issues with the operation of these cards.

I do not know if the isolator will cause problems with other USB standalone modules.

This post is but a primer.  For additional information, refer to the Phidgets website.  Note I am not affiliated with Phidgets in anyway.

Glossary

CPS – Computer Power Supply.
PCI Card – Computer bus for connecting various hardware devices.

Friday
Jan012016

Circuit Breakers For Self Preservation

Following on in the same theme as my earlier post 'Are You Protected - Power Surges', we discuss in more detail the various circuit breakers that can be used in a simulator setting.  Additionally, it is stressed that electricity can kill and a qualified electrician should be contacted prior to implementing anything suggested below.

LEFT:  Selection of Eaton Memshield MCB circuit breakers. 

My thanks to Dave Egkkman (flight simulator enthusiast based in the United Kingdom) who has written this article.  I think the content adds considerably to my earlier post and I am grateful to Dave for writing and allowing it to be posted here.

Circuit Breakers and Fuses 

It is a common misconception that fuses and circuit breakers are there for personnel protection. It is very important to understand that this is not the case.

It can take as little as 0.03A to kill a human being, that’s 30mA! So, if you have a circuit protected by a 30A fuse/circuit breaker, it will allow 1000 times more current to flow than it takes to kill, before it breaks the circuit and stops the current flow.

Fuses and circuit breakers (protective devices) are there to protect the cabling in an electrical circuit from damage by overload. This is achieved by installing a suitably rated circuit breaker at the beginning of a circuit. The rating of the protective device will be calculated to protect the lowest rated cable in the circuit, by stopping the flow of current in an overload situation before the current flow exceeds the current rating of the cable.

A common scenario in the UK is the use of 13A fuses in plugs. In domestic plugs in UK, the plug can take a variety of fuses rated from 1A to 13A. Often loose plugs are supplied fitted with a 13A fuse or, if a fuse ‘blows’ the user will commonly fit a 13A fuse as a replacement. However, if the appliance is a lamp standard, the cable from the plug to the electrical appliance could be rated at 6A or less.

So, in the event of a fault developing that allows 10A to flow, the fuse will not break the circuit, but the cable could well overheat and catch fire, and still the fuse may not break the circuit.

Fuses

A fuse is simply a piece of small wire designed to melt and break the circuit if more current flows than the fuse wire is designed to allow to flow.

In some cases, faults can occur in which the current may not be large enough to melt the fuse but enough to seriously harm the user of the electrical appliance. Circuit breakers generally offer better protection

Circuit Breakers

For domestic installations there are three main types of circuit-breakers.

1.         Miniature Circuit Breaker (MCB)

2.         Residual Current Circuit Breaker (RCCB) or Residual Current Device (RCD).

3.         Residual Circuit Breaker with overload (RCBO)

Miniature Circuit Breaker (MCB)

The MCB is a protective device typically used where a fuse would have been. MCBs are quicker to respond than fuses, are more reliable, more sensitive and can be reset once the fault has been cleared, the problem identified and fixed.

LEFT:  Protec 63A 363-2C-6kA Triple Pole MCB circuit breaker.

There are many different configurations of MCBs, which we won’t go into here. We should however consider the three different ‘Types’ that are available. All 3 MCB types use a magnetic fault protection, which trips the MCB within one tenth of a second when the overload reaches a set level.

How a MCB Works

Basically, the live input cable is wound around an iron core. As current flows a magnetic Field is generated. If the magnetic field reaches a pre-set level, an iron latch is pulled towards the iron core (magnet) and breaks the circuit.

In normal domestic use a Type B MCB will be used. A Type B breaker will trip between 3 and 5 times full load current.

For electrical loads that have a high inrush current when they are switched on, a Type B breaker is likely to trip as it ‘sees’ the inrush current as an overload.

A Type C breaker trips between 5 and 10 times full load current. This allows the MCB to withstand the initial inrush current, whilst still providing overload protection in normal use.

A Type D breaker trips between 10 and 20 times full load current, typically used where high inductive loads are present such as motors and transformers.

For those with problems of an MCB (or a fuse) tripping when turning on equipment, a Type C breaker may be the answer. Selecting the correct Type and rating of breaker is not an arbitrary decision. An electrically qualified person should make this decision.

Whichever MCB type is used, it is extremely dangerous to cut corners by using inferior quality devices, therefore they should only be bought from a reputable supplier. Copy and cheap MCBs have been found to have no copper/nickel/silver contacts within them, just steel. Upon introducing a fault, the contacts simply weld together, the consequences are obvious. Don’t go cheap.

Residual Current Device

A residual current device IS designed to offer personnel protection. RCDs are used in combination with fuses and MCBs.

LEFT:  ETI 25A 30mA RCD 2 throw circuit breaker.

Residual current circuit breakers work by comparing the current entering the appliance via the live input with the current leaving the appliance through the neutral.

How a RCD Works

The live wire and neutral wire within the device, are wound around iron cores in opposite directions. When the appliance is working correctly ALL the electrical current entering the appliance via the live wire, exits the appliance through the neutral wire. The magnetic fields generated around the iron cores cancel out.

In the event of a fault some of the electric current will flow through the earth wire, casing of the appliance or in the absence of proper earthing through the body of the user. This results in an imbalance between the current entering the appliance through the live wire and the current exiting through the neutral wire.

This difference in electrical current is called the residual current and it is what causes the device to break the circuit.

Residual Current Circuit Breakers have the advantage of being highly sensitive with a very quick response time.

There are various ratings of RCDs. Typically, in domestic use a 30mA RCD will be used, but 10mA is also common. Selecting the correct Type and rating of RCD is not an arbitrary decision. A qualified person should make this decision.

It is not unusual for people to complain that RCDs suffer from nuisance tripping. If an RCD is tripping there is a problem, the problem should be identified and corrected. If an upstream RCD is tripping, rather than the local RCD, for example the RCD in the house trips and the one in the out building does not, then the configuration of the circuit is incorrect. These issues should be addressed by, yes you guessed it, a suitably electrically qualified person. Issues of disconnection times, voltage drop, resistance of the earth path all need to be considered.

Residual Circuit Breaker with overload

A residual circuit breaker with overload (RCBO) protection is a device that combines overload and personnel protection.

They are often used where there is not enough space for an MCB and RCD in one consumer unit / fuse board.

Disclaimer

This information is provided to offer guidance only and hopefully to suggest when an electrically qualified person should be approached for guidance. It is not comprehensive and only scrapes the surface of the subject of electrical protection.

I don’t want to come across as ‘holier than thou’ but, I really don't wish to be drawn into offering guidance to people about which and what protective devices should be used for their particular installation. I don't even agree with DIY companies selling fuse boards, MCBs etc. I'm hoping my words will encourage folks to seek professional advice from a local engineer/electrician who can assess their own situation. It's not the same as deciding which interface card to use for TQ servo activation!

All electrical work must be carried out by a qualified engineer/electrician and this post is not suggesting otherwise.

Glossary

A - Amp
mA - Milliamp

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