Shower, what cable size and braker?

[Stephenmunt]

Hi guys. I was wondering what size cable and braker I'd need for an electric shower.

Just out of intrest am I close in guessing as follows:

The shower unit is an 8.5kw. Total meters to C/U is about 15meters. 10mm cable, 40A fuse. the cable will be solely for the shower supply, and RCD 1way consumer unit will be put in the attic above the bathroom, leading to a single or bouble? Pull cord and then to the shower.

OK how bad was my guess? Lol

 

[nicebutdim]

10mm cable might be suitably protected at 40A, but equally it may not.

How would you supply this one way board and why would you fit it in an attic?

 

[Stephenmunt]

10mm cable might be suitably protected at 40A, but equally it may not.

How would you supply this one way board and why would you fit it in an attic?

It seems that's 8.5kw is in the middle of 6mm and 10mm so I'm stuck there. Also my C/U is in a bit of a state so while I save some money to get it upgraded I was thinking of playing it safe with an RCD UNIT along the way. And the attic is quite clean and space for it to go in there.

What are your thoughts

 

[Other_Tucker]

8500w / 230v = 37A breaker. We rule that 32A and below is 6mm, above 7,360w is 40A and 10mm for all council properties. I'd always follow that advice.

Watch out for insulation, I've been having 10mm cable fail calculations when 30cm of insulation was added on top of existing shower cables in lofts. 500mm of the cable covered in insulation is a derating factor of 0.5.

Edit: For 7.2kw showers and below, not run near insulation, you can get away with 6mm. We always run 10mm now in case tenants upgrade their own showers or insulate their lofts

 

[westward10]

It's "breaker" as in it breaks a circuit, not "braker".

 

[Stephenmunt]

8500w / 230v = 37A breaker. We rule that 32A and below is 6mm, above 7,360w is 40A and 10mm for all council properties. I'd always follow that advice.

Watch out for insulation, I've been having 10mm cable fail calculations when 30cm of insulation was added on top of existing shower cables in lofts. 500mm of the cable covered in insulation is a derating factor of 0.5

Nice one, thank you. still get stuck on the mm size and cable insulation size lol

 

[Stephenmunt]

It's "breaker" as in it breaks a circuit, not "braker".

Sorry. I'm a little dyslexic

 

[nicebutdim]

It seems that's 8.5kw is in the middle of 6mm and 10mm so I'm stuck there. Also my C/U is in a bit of a state so while I save some money to get it upgraded I was thinking of playing it safe with an RCD UNIT along the way. And the attic is quite clean and space for it to go in there.

What are your thoughts

Can you explain what you mean by this?

An attic seems like a less than ideal location to locate a board, but I was more interest in how you plan on supplying it? If you intend fitting a 40A MCB to the existing board, I'd consider this to also be less than ideal.

 

[Stephenmunt]

Can you explain what you mean by this?

An attic seems like a less than ideal location to locate a board, but I was more interest in how you plan on supplying it? If you intend fitting a 40A MCB to the existing board, I'd consider this to also be less than ideal.

I have an unused cable running from my attic to my main C/U 10mm cable. This was previously used for a boiler. I was guessing that this cable that is currently on a 16A breaker could be changed for a 40A

 

[nicebutdim]

I have an unused cable running from my attic to my main C/U 10mm cable. This was previously used for a boiler. I was guessing that this cable that is currently on a 16A breaker could be changed for a 40A

The cable terminated in Wago connectors in your other thread?

 

[Other_Tucker]

It seems that's 8.5kw is in the middle of 6mm and 10mm so I'm stuck there. Also my C/U is in a bit of a state so while I save some money to get it upgraded I was thinking of playing it safe with an RCD UNIT along the way. And the attic is quite clean and space for it to go in there.

What are your thoughts

You should not be installing an RCD unit 'along the way'. Change your CU for an 18th edition metal clad RCBO SPD protected board, before any other DIY electrics. If you can't do that properly don't electrocute your shower

 

[Stephenmunt]

The cable terminated in Wago connectors in your other thread?

Yes

 

[nicebutdim]

Yes

It's not 10mm - at the very most that cable's CSA is four times smaller than you think and possibly even smaller again.

Please don't take this the wrong way, but what stage are you at as a trainee electrician? I don't think this is something you should be attempting at this point.

 

[mainline]

It's not 10mm - at the very most that cable's CSA is four times smaller than you think and possibly even smaller again.

The conductors aren't solid, so it's bigger than 2.5mm
Probably 4mm, the wago 221s will take 6mm.

 

[nicebutdim]

The conductors aren't solid, so it's bigger than 2.5mm
Probably 4mm, the wago 221s will take 6mm.

Still not 10mm, but...

Here's the post with image. While detail is difficult to ascertain, the line conductor certainly appears to be solid. Looking further into this, it's quite clear the connectors are 221-412 from data printed on them, which would accept a maximum of 4mm CSA.

I probably should have added this three weeks ago and saved you some time.

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