Voltage drop. Would you be concerned?

Hi all

I have a job to supply a new 2 way board in outhouse. Am planning on running it from a 32 Amp MCB in 4mm twin and earth to adaptable box to outside and then 4mm SWA from there. The twin and earth is 7 metres and the SWA about 25 metres. My calcs for voltage drop comes in at  4.7% but this is at the full load of the 32 amp MCB. Obviousky 4.7% is higher than the 3% stipulated for lighting. Would others be concerned about this and increase cable to 6mm. Thanks

YES.

^concur^
 

why wouldn’t you? 

^^ agree

why the twin and earth then SWA? Surely better with 1 cable

yes... you know your cable design doesnt comply, why continue with it?

Why do you think the regs are there for, so you can just ignore them as you don't think there right.

The people who right them are a lot more qualified than you.

septiclecky said:

The people who right them are a lot more qualified than you.

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to be fair, thats probably questionable when you look at some of them...

Thanks all for confirming. Customer has sourced some 4mm armoured and is hopeful of using that looks like will have to break the bad news. I just thought might possibly be some leeway as although design of circuit is 32 amps the likelihood of this ever being reached is pretty slim. But best to air on side of caution I suppose. 

Murdoch said:

^^ agree

why the twin and earth then SWA? Surely better with 1 cable

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It's being run in surface trunking before going outside Murdoch

DaveS79 said:

Customer has sourced some 4mm armoured and is hopeful of using that looks like will have to break the bad news. 

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tell the customer he can have a 20A Max design load with his 4 mm or fit 6mm and buy more cable

why does the client think he needs 32A?

septiclecky said:

Why do you think the regs are there for, so you can just ignore them as you don't think there right.

The people who right them are a lot more qualified than you.

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Get back in your box septic. That's part of the reason I posted question to see others thoughts that are more qualified/experienced than me and see if missing anything with my calcs or anything else I need to consider

Murdoch said:

tell the customer he can have a 20A Max design load with his 4 mm or fit 6mm and buy more cable

why does the client think he needs 32A?

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The 32 amp call is mine Murdoch. Don't feel to comfortable giving him 20 as said could be various appliances down there washine machine etc and may use it for as bit of a workshop as well

DaveS79 said:

The 32 amp call is mine Murdoch. Don't feel to comfortable giving him 20 as said could be various appliances down there washine machine etc and may use it for as bit of a workshop as well

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then maybe the client would have been wise to have sourced 6mm cable??

DaveS79 said:

The 32 amp call is mine Murdoch. 

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on what basis ? That’s quite a load. . What is this outhouse going to be used for?

Murdoch said:

on what basis ? That’s quite a load. . What is this outhouse going to be used for?

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I just said that above Murdoch "The 32 amp call is mine Murdoch. Don't feel to comfortable giving him 20 as said could be various appliances down there washine machine etc and may use it for as bit of a workshop as well"

DaveS79 said:

I just said that above Murdoch "The 32 amp call is mine Murdoch. Don't feel to comfortable giving him 20 as said could be various appliances down there washine machine etc and may use it for as bit of a workshop as well"

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could be various appliances ..... you need to get your customer to make decisive decisions and, imho, you need to get used to being firmer with clients

so you use his 4mm cable - would you test it before you first fixed it ?

Murdoch said:

could be various appliances ..... you need to get your customer to make decisive decisions and, imho, you need to get used to being firmer with clients

so you use his 4mm cable - would you test it before you first fixed it ?

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Noted need to pin them down more in future on what using it for and make more of a point that I source my own materials. 

I have never "understood" 4mm cable.  I don't personally use it.  Why would you?  In theory it;s good for 32A under certain circumstances.  Okay. Simple question.  Would ANYONE here use 4mm for a 7kW electric shower?  No I didn't think so.  So if not, why would you use 4mm for anything else fed from a 32A mcb?

DaveS79 said:

Noted need to pin them down more in future on what using it for and make more of a point that I source my own materials. 

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if customers try and supply kit, other than lights / hobs/ ovens etc

1. I tell them I will charge my hourly rate for any down time due to wrong or faulty or missing material

2. I increase my hourly rate ....

Murdoch said:

if customers try and supply kit, other than lights / hobs/ ovens etc

1. I tell them I will charge my hourly rate for any down time due to wrong or faulty or missing material

2. I increase my hourly rate ....

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well to paraphrase what Murdoch is saying, ‘you wouldn’t go into Dfs or the like with a roll of fabric and say I’d like a suite in this please!!’ 

DaveS79 said:

Hi all

I have a job to supply a new 2 way board in outhouse. Am planning on running it from a 32 Amp MCB in 4mm twin and earth to adaptable box to outside and then 4mm SWA from there. The twin and earth is 7 metres and the SWA about 25 metres. My calcs for voltage drop comes in at  4.7% but this is at the full load of the 32 amp MCB. Obviousky 4.7% is higher than the 3% stipulated for lighting. Would others be concerned about this and increase cable to 6mm. Thanks

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If you have calculated 4.7% I would be guessing you are using 240v as your nominal volatge?

Think you should use 230V?

But even so...

Have you even considered what current would be compliant over 25m+7m 4.0mm..   ( + whatever few metres you also have on your final circuits?)

Even a 20A MCB is just on the 3% limit..

NOW..   if you tell your customer you are only doing a 16A outbuilding supply.....

BUT if you really want a 32A supply....

Have you actually done calc's for 6.0mm over 32m?

Technically I think you will find that is just over 3% when calc'd using either 230v or 240v...

How big is the outbuilding?

How long will the final circuits in there be?

Guinness