Why 2m max from EHU to the consumer unit? (1 Viewer)

Nov 19, 2021
21
161
Nottingham, UK
Funster No
85,513
MH
Building a PVC
Exp
10 years
I've seen this mentioned a few times in various places but have never got to the bottom of why it is recommended (required?) that the consumer unit should be no more than 2 metres from the EHU. Can any wizards enlighten me, please?....
I would really like to have to have the following arrangement (mostly for reasons of convenient and tidy cabling, to get the consumer unit internally accessible**):-

EHU----(30cms)---->AVS30------(2m)----->Sargent 155 Consumer Unit

** the consumer unit was originally going to be next to the EHU in the garage but a series of changes to the design and desire have led to a change of thinking.

Thoughts and advice welcome and appreciated (If I have to relocate the EHU or the Sargent, then so be it!).

:)
 
Sep 9, 2019
884
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Runcorn
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Autotrail Apache 632
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From a logic point of view I can’t see any reason to limit the distance between EHU and consumer unit within the potential maximum cable runs in a van. How far can it reasonably be? 3 metres? The supply to the EHU on the side of the van could potentially be 2 lots of 25 metre extension leads from a socket on the site’s supply consumer unit. Another couple of metres inside the van is going to be negligible in terms of voltage drop compared to the first 50 metres! Sounds like a lot of Hocum to me. As long as the supply cabling from your EHU in the side of the van is capable of handling at least 16amps (the maximum rating of the socket, the incoming on/off main switch on the consumer unit and the maximum supply from the campsite) then you will be fine. Two caveats…. 1) Don’t cover it up with anything like duvets, towels, clothes or blankets, it needs free air to keep cool and retain its current and voltage carrying characteristics. 2) Might be a legality issue I’m currently unaware of, but I’m sure a more learned spark will be along soon to quote chapter and verse from BS7671 18th edition+A2, which is official speak for “The Electrical Regs”

Hope that helps!

Russ
 
Feb 27, 2011
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You want the consumer unit as close to where the EHU enters the vehicle to minimise the length of cable inside the vehicle potentially unprotected by the vehicles RCD.

Example:
If a fault develops on the cable between the EHU entry point and the consumer unit, and the sites protection is not good say for instance the earth has been disconnected. There is potential for your vehicle chassis to become live. This could injure or kill any one touching your vehicle with their feet on the ground.

By minimising the distance between the EHU entry point and the consumer unit you are minimising the length of "risk". You should also as a matter of safety double insulate the cable by running it in conduit. I personally use copex/kopex flexible conduit in my self builds for this job.
 
Apr 27, 2016
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You want the consumer unit as close to where the EHU enters the vehicle to minimise the length of cable inside the vehicle potentially unprotected by the vehicles RCD.
This is true, and you may also want the 12V distribution box to be near the leisure batteries, which may not be near the EHU inlet. This is a problem when the mains trips and the 12V fuses are all in the same box, as in Sargent units. You could fit a small box with a 16A RCBO near the EHU inlet. And even fit a few MCBs and run your mains wiring from there instead of the Sargent unit.

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ctc

Oct 12, 2015
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I don't know how many people have died from electric shocks in their vans but I think no matter what length cables the risk is nonexistent to minute. You are far more likely to be killed in your own home by a tea cosy (one in Suffolk some years ago)
 
Apr 27, 2016
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I don't know how many people have died from electric shocks in their vans but I think no matter what length cables the risk is nonexistent to minute. You are far more likely to be killed in your own home by a tea cosy (one in Suffolk some years ago)
This always seems to happen when a problem is successfully solved. People then start saying there never was a problem in the first place.
 
Feb 27, 2011
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I don't know how many people have died from electric shocks in their vans but I think no matter what length cables the risk is nonexistent to minute. You are far more likely to be killed in your own home by a tea cosy (one in Suffolk some years ago)

As autorouter says. Why do you think so few people die from electric shocks these days? It is because of the very regulations and guidelines you are now mocking.
 

ctc

Oct 12, 2015
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As autorouter says. Why do you think so few people die from electric shocks these days? It is because of the very regulations and guidelines you are now mocking.
Look at the figures, there has been little or no reduction in deaths from electric shock from the 1930's. All that's happened is plug tops and sockets are now a little more child proof , my youngest grandchild can open the shutters on a socket with ease, he's 6. So there is a small reduction in child deaths, adults remain about the same. Your library can get the Observation Society's book listing the older figures, the latest are available in council reports which is where the famous tea cosy death comes from.
 
Feb 27, 2011
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Look at the figures, there has been little or no reduction in deaths from electric shock from the 1930's. All that's happened is plug tops and sockets are now a little more child proof , my youngest grandchild can open the shutters on a socket with ease, he's 6. So there is a small reduction in child deaths, adults remain about the same. Your library can get the Observation Society's book listing the older figures, the latest are available in council reports which is where the famous tea cosy death comes from.
Not getting into a pointless debate on this. Your grandchild's ability to bypass the shutters is not relevant. Nor is the deaths in electric shocks in the 1930s.

If you are happy to ignore safety guidelines have at it, on your own head. But please do not suggest to others that they can safely ignore the guidelines.

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bigtwin

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Oct 29, 2009
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What exactly does success look like? I'd call that a successfully solved problem, considering the increase in usage of electric appliances since the 1930s.

and not forgetting the increase in the population (noting that this can be considered to be encompassed within your use of ‘increase in usage’ 👍).

Ian
 
Jul 29, 2007
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If you run it in armoured it used to be the that you could run it much further, not up on latest reg so may have changed.
 
Feb 27, 2011
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If you run it in armoured it used to be the that you could run it much further, not up on latest reg so may have changed.
The tails as they are called should not be over 3 meters in a domestic property. Not sure about armoured though. I am not up to date on the regulations as I have no desire to go back on the tools.


But that is a domestic property. For a vehicle especially a leisure one. I want the RCD as close to the incoming EHU point as possible and the cable to be protected.

I also don't like seeing it where the EHU cable runs within a cupboard or cabinet accessible by the owner without it being heavily protected. It only takes one person to throw something sharp/heavy in to damage the cable and cause issues before it gets to the RCD.

There is also the fire risk not just electric shock risk.
 

Hoovie

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May 16, 2021
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Not getting into a pointless debate on this. Your grandchild's ability to bypass the shutters is not relevant. Nor is the deaths in electric shocks in the 1930s.

If you are happy to ignore safety guidelines have at it, on your own head. But please do not suggest to others that they can safely ignore the guidelines.
As they say, you can't legislate against stupidity.

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Minxy

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Aug 22, 2007
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You are far more likely to be killed in your own home by a tea cosy (one in Suffolk some years ago)
Can you point me to this as I'd like to buy a deadly tea cosy for someone and want to get the right one! 😄
 

Hoovie

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May 16, 2021
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Can you point me to this as I'd like to buy a deadly tea cosy for someone and want to get the right one! 😄
Think "Q" can supply one for the new 007 film "Granny Bond", along with plutonium tipped Knitting Needles
 
OP
OP
3
Nov 19, 2021
21
161
Nottingham, UK
Funster No
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Building a PVC
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10 years
Many thanks for the replies. :)
As I read it so far there is no actual 'requirement' that the max length is 2 metres but certainly risk (reduction) and good practice lead to the 'recommendation' that the RCD is as close to the EHU as possible - as per the words of Grommet and others, I have always been mindful of the cautionary words in the Victron guide on wiring 240V (so my wires are double-insulated with conduit - though I like the idea of armoured conduit - and largely separated from people and metal by at least 1 if not 2 sheets of plywood).
I like the idea of a separate RCD adjacent to the EHU - because I would like to keep the Sargent internally accessible, rather than having to keep opening the back doors for access.
I'll keep watching and thinking.
Thanks folks
 
Jul 29, 2007
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The tails as they are called should not be over 3 meters in a domestic property. Not sure about armoured though. I am not up to date on the regulations as I have no desire to go back on the tools.


But that is a domestic property. For a vehicle especially a leisure one. I want the RCD as close to the incoming EHU point as possible and the cable to be protected.

I also don't like seeing it where the EHU cable runs within a cupboard or cabinet accessible by the owner without it being heavily protected. It only takes one person to throw something sharp/heavy in to damage the cable and cause issues before it gets to the RCD.

There is also the fire risk not just electric shock risk.
When I rewired the shop around 2002 the tails went into a 3 phase isolator, from there I ran an amoured cable up to the floor above and around 20' to the rear wall to the consumer unit in a cupboard.
I don't think there was a limit on how long the amoured could be at that time.
 
Apr 27, 2016
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When I rewired the shop around 2002 the tails went into a 3 phase isolator, from there I ran an amoured cable up to the floor above and around 20' to the rear wall to the consumer unit in a cupboard.
I don't think there was a limit on how long the amoured could be at that time.
Armoured cable is fine for hookup posts and fixed installations, but I don't think it's suitable for vehicles. Although armoured cable is stranded, there's typically only 7 strands, but flexible cable is typically 30 to 50 strands so it can withstand vibration better. I appreciate the armour would protect it along most of its length if properly supported, but at the ends it would be vulnerable.

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Feb 27, 2011
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When I rewired the shop around 2002 the tails went into a 3 phase isolator, from there I ran an amoured cable up to the floor above and around 20' to the rear wall to the consumer unit in a cupboard.
I don't think there was a limit on how long the amoured could be at that time.
I did some checking and it appears that 3 meters is the recommended limit for tails. If there is no choice but to exceed this then there should be a fused isolator. Some seem to suggest SWA is also required but it it is confusing.

Armoured cable is fine for hookup posts and fixed installations, but I don't think it's suitable for vehicles. Although armoured cable is stranded, there's typically only 7 strands, but flexible cable is typically 30 to 50 strands so it can withstand vibration better. I appreciate the armour would protect it along most of its length if properly supported, but at the ends it would be vulnerable.
Agreed. armoured/swa in a vehicle would not be required or practical. If someone wants this kind of level of protection probably steel conduit would be a better solution with stranded multicore wires inside? But I can't think of a leisure vehicle where this level of protection would be necessary?

Also unless it was just a straight run, armoured would be a pain to install even if it was the best solution.
 
Sep 17, 2017
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My 2020 registered German van doesn't follow this 2m rule. The hookup is in the middle of the van on the left side. The consumer unit is in a cupboard at the back on the right. It must be using at least 5m of cable to get there.
 
Feb 27, 2011
14,842
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UK
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Self Build
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My 2020 registered German van doesn't follow this 2m rule. The hookup is in the middle of the van on the left side. The consumer unit is in a cupboard at the back on the right. It must be using at least 5m of cable to get there.
German van. they have different regulations to the UK?
 
OP
OP
3
Nov 19, 2021
21
161
Nottingham, UK
Funster No
85,513
MH
Building a PVC
Exp
10 years
Lol
ok - 'recovering the thread' (and apologies for the more very specific question) - if I go with Autorouter's suggestion of a 16A RCBO near the EHU inlet (it can go right next to it in this instance), would the most sensible thing be to place this BEFORE the AVS30?
Thanks
 
Feb 27, 2011
14,842
76,965
UK
Funster No
15,452
MH
Self Build
Exp
Since 2005
Lol
ok - 'recovering the thread' (and apologies for the more very specific question) - if I go with Autorouter's suggestion of a 16A RCBO near the EHU inlet (it can go right next to it in this instance), would the most sensible thing be to place this BEFORE the AVS30?
Thanks
I don't know what the AVS30 is or what they recommend. But if you can't put the main consumer unit next to the EHU inlet and are putting in an additional RCD or RCBO then if it were me I would put it right next to the EHU and place the AVS30 after.
 
Oct 28, 2022
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Look at the figures, there has been little or no reduction in deaths from electric shock from the 1930's. All that's happened is plug tops and sockets are now a little more child proof , my youngest grandchild can open the shutters on a socket with ease, he's 6. So there is a small reduction in child deaths, adults remain about the same. Your library can get the Observation Society's book listing the older figures, the latest are available in council reports which is where the famous tea cosy death comes from.
Think your overlooking the uptake of usage in electricity since the 1930s,

seriously trust the regulators on this, they know what they are talking about…

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