Question (Electrical guru,s)

[gareth lacey]

I have 8 carling rocker switches  with power coming through 8 thermal overload contacts, all switches require led grounding plus grounding for load, can i loop all switches with grounding for led and load or should i go for individual grounding to terminal ground block

Cheers Gareth

[RFguy]

The answer- Ground individually or use a tagged bus bar.

There is a good reason to ground individually to a bus bar, that is well grounded.

 

This way there are no common ground currents between devices.

 

Common ground currents can be a source of noise injected into system- that is SHARING a ground with currents from other devices. 

Current times resistance = voltage. Voltage injected = Noise.

 

Additionally, with a single ground, looped along, everything is hanging on one ground, not great either.

 

How does this work ? imagine a irrigation system with  the returns for many sprinklers all series up in a diasy chain of Ts. if one sprinker stops and starts, there will be a measurable pulse put into all the other sprinker water flows because of a common flow.  This happens because the pipes have some resistance. Same with the currents and wire that has resistance. 

 

Many systems use a bus bar tag- a strip of copper with tabs coming out at the right spacing so the switch can be screwed directly to a bus bar tab. How is this different you might ask to just looping them next to next ? The bus bar is essentially perfect ground and no resistance.  Loops wires each to each adds an additional two contact joints plus crimps plus wire resistance for each hop. Current times resistance = voltage. Voltage injected = Noise.

 

Edited January 21, 2021 by RFguy

[gareth lacey]

Thanks rfguy thats what i thought but asking someone who knows is better than taking a stab in the dark cheers Gareth 

[RFguy]

Electrically, that is how it should be done... but I dare say looping them up might be acceptable and often done, I dunno, I would have to look up the FAA bible .

[gareth lacey]

[gareth lacey]

Just now, gareth lacey said:

Here is my bus for  ground and power  thoughts? Thanks for your replies

[RFguy]

Use a BUS BAR COMB  :

 

 

[RFguy]

your earth bus is satisfactory, even if it is designed for  commercial and domestic power, that will do the job, but for V+  I would suggest using bus combs instead of multi loops. cut / saw them to length. 

and remember, not too many devices per circuit- the wiring for any single  single circuit has to be capable to blowing the circuit breaker for the circuit without catching fire...

 

Look up AC 21-99

 

 

Edited January 21, 2021 by RFguy
Look up AC 21-99

[gareth lacey]

Each switch is per single use other than 2 usb and strobes, radios tx, ems ,flaps, trim,etc all single use cheers Gareth 

[gareth lacey]

Where would i get a bus comb from ,looking at ebay mostly from US and COSTLY

cheers gareth

 

[Yenn]

That Bus looks good, but I wonder about the bus bar comb. If you run say six circuits to the bus bar comb, there will have to be a connection to the battery that is bigger than the tags shown.

I made my own earth bus on one plane and all was well, but extra things got added and eventually I notice the wire from the bus to the battery was showing signs of overheating. Lucky I spotted and silly that I didn't anticipate it.

[RFguy]

[

Edited January 21, 2021 by RFguy

[RFguy]

OK.

does the single breaker feeding any  of those  those  exceed the wire rating  ?

EXAMPLE : 40A breaker, for 4 x 10A devices. In the even of a short say, due to a crush on the wires to one of those devices , the wiring MUST be able to withstand the current required to comfortably trip the breaker (without producing a fire, melting other wires, fuel hose etc) 
This usually leads to a requirement for hefty wire everywhere, which is why items may be further divided up with small breakers.

This is defined SOMEWHERE.  anyone know? If you look up the harness rating for wiring, that will give you the answer...
"Table 1-I-1 Current Rating Of Wires In Amps (SAE AS 50881)" in AC21-99 is a place to start.

Edited January 21, 2021 by RFguy

[Yenn]

I made my own bus similar to a bus comb, from sheet copper, cut to take 6mm female spade connectors.

[RFguy]

In 

AC 25.1357-1A - Circuit Protective Devices (faa.gov)

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_25_1357-1A.pdf

 

there is a list of regulations and advisory circulars for reference at the end of that , very useful.

 like AC25-16

 

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_25-16.pdf

 

[gareth lacey]

18 minutes ago, RFguy said:

OK.

does the single breaker feeding any  of those  those  exceed the wire rating  ?

EXAMPLE : 40A breaker, for 4 x 10A devices. In the even of a short say, due to a crush on the wires to one of those devices , the wiring MUST be able to withstand the current required to comfortably trip the breaker (without producing a fire, melting other wires, fuel hose etc) 
This usually leads to a requirement for hefty wire everywhere, which is why items may be further divided up with small breakers.

This is defined SOMEWHERE.  anyone know? If you look up the harness rating for wiring, that will give you the answer...
"Table 1-I-1 Current Rating Of Wires In Amps (SAE AS 50881)" in AC21-99 is a place to start.

using Tefzel wire sizing for each component mostly 20 22 g 1 overload switch is for battery isolator ,this feeds the on off switch to the bus  ,using 1x40 amp 3x10 amp,4x5 amp overload switches i can change these if required,my dash hinges back so i can access all electrical components, also access hatch 300x200 behind the fire wall

 

[RFguy]

rightio, sounds fine.  so 40A is feeding the 3x10A and 4 x 5A ?. just bne sure your CPD is rated at not more than 85% of the max current, as they can degrade a bit with age and trip early.

 

sounds like  you have good access. 

[gareth lacey]

5 hours ago, gareth lacey said:

Here is my bus for  ground and power  thoughts? Thanks for your replies

[gareth lacey]

[RFguy]

on the right hand side, the cascaded white loops, what is that ?

 

[gareth lacey]

Bus for power to accessories just looped to each contact only using 5

[RFguy]

It's not the way things should be done, but , It will work  that way-  put the highest power consumers at the 'top' of the tree.

Ideally  needs to be copper  comb...