8.5kw shower wires in 4mm, burnt terminals

[robo83]

Just arrived at a job, 45amp shower isolator completely burnt out.

Checked cable and it's 4mm tne in trunking to 8.5kw triton riba shower on a 32amp mcb. Cable run is 5meters.

This was a new circuit installed only a few months ago. I expect loose connection on isolator causing burnt terminals.

I am going to request cable uprated to 6mm, anyone else make any sense why a 4mm was used?

 

[Octopus]

what type of switch was it? Pull cord or wall mount?

FWIW 4 mm wasn't big enough to start with.

 

[Pete999]

That's all he had in the Van, or quite obviously he has miscalculated.

 

[Octopus]

or quite obviously he has miscalculated.

Or did he think at all - 4mm T&E was never going to be big enough IMHO

 

[Pete999]

Ah sid it I'll stick some 4mm2 in, it'll be OK til it burns out, I'll be long gone by then, or something to that effect, or he's aDilbert.

 

[Des 56]

He put the 4.0mm on a 32 amp mcb,it was supplying a 7KW unit, its since been changed for the 8.5KW by the user

Fantasy thinking I suppose but it often happens,think of 6.0mm and the purchases of the monster energy guzzlers by the ladies swooning over their size in B+Q

 

[Pete999]

He put the 4.0mm on a 32 amp mcb,it was supplying a 7KW unit, its since been changed for the 8.5KW by the user

Fantasy thinking I suppose but it often happens,think of 6.0mm and the purchases of the monster energy guzzlers by the ladies swooning over their size in B+Q

Deleted

 

[Octopus]

Who in their right mind would run in a new dedicated shower circuit in 4mm?

 

[telectrix]

Who in their right mind would run in a new dedicated shower circuit in 4mm?

someone who calculated that it was adequate for the load it served.

 

[robo83]

Just spoke to landlord.

Landlord purchased shower first and informed her other electrican what she had purchased, he then went and installed supply.

 

[robo83]

This was condition of terminals when I arrived, MCB & RCD still in closed position.

 

[Octopus]

Just spoke to landlord.

Landlord purchased shower first and informed her other electrican what she had purchased, he then went and installed supply.

In which case landlord needs to get said spark back to replace switch and cable ......

 

[Rpa07]

Shakes head!

 

[Pete999]

This was condition of terminals when I arrived, MCB & RCD still in closed position.

View attachment 37612

Oh nice

 

[Rpa07]

And it's not the neutral this time!

 

[westward10]

I suspect the root cause of this was a loose connection and not conductor csa although it is obviously undersized.

 

[robo83]

I've told llthe landlord to get other electrican to call me if he has any issues returning to sort, also when I undid the isolator Fascia the cables just fell out the back.

I checked over the board before I disconnected the supply and some of the terminals were LOOSE :/

 

[telectrix]

but was not undersized for the 7kW shower, and was suitably protected with a 32A MCB. a bit like the chandelier i just repaired for a customer. 105VA transformer supplying 10 x 10w G4 lamps. he'd fitted 10 x 20w G4s and wondered why the transformer failed.

 

[robo83]

The landlord said they told the electrican what shower they were getting. And the sparks installed it with the cable, he must have known it was 8.5kw.

 

[telectrix]

The landlord said they told the electrican what shower they were getting. And the sparks installed it with the cable, he must have known it was 8.5kw.

even so, the 4mm would have handled that 8.5kW. it's down to poor terminations.

 

[Octopus]

^^ even if I knew it was going to be a 7kw shower, I would still have fitted 6mm cable

 

[The Ghost]

B+Q

Q+Q more like

 

[Ian1981]

even so, the 4mm would have handled that 8.5kW. it's down to poor terminations.

May depend upon the reference method used for installation as 4mm installed in trunking de rates to around 30 amps

 

[Lee42]

I've told llthe landlord to get other electrican to call me if he has any issues returning to sort, also when I undid the isolator Fascia the cables just fell out the back.

I checked over the board before I disconnected the supply and some of the terminals were LOOSE :/

Sounds like he had plastic wrists

 

[Lee42]

I had a similar situation yesterday.
Reports of shower isolator getting hot. Go to check it out. 6mm installed last year supplying a 9.5kw shower. Burnt out connections.
I would always install a 10mm if wirring for a new shower.

 

[davesparks]

^^ even if I knew it was going to be a 7kw shower, I would still have fitted 6mm cable

Which is fine, and if you wish to do that then there is nothing preventing you from doing so. But if the calculations show that 4mm is suitable then you cannot criticise someone for installing 4mm, whatever your personal preference in the situation.

 

[westward10]

10.0 doesn't prevent loose connections and burnt conductors.

 

[Lee42]

10.0 doesn't prevent loose connections and burnt conductors.

You're quite right.
I always tighten connections. Leave them a minute to settle then u can normally get another quatre turn on them.
The reason we always wire a new shower supply in 10mm, is so the customer has some flexibility when coming to choose a shower.
And like ive seen before, when the customer decides on him/her self to uprate the shower to a 10.5kw. Not realising the existing 6mm will not be adequate. (Normally a trip back to b and q for them)
I would always recommend not installing a electric shower, much better of a combi, but needs must sometimes

 

[Wilko]

I had a similar situation yesterday.
Reports of shower isolator getting hot. Go to check it out. 6mm installed last year supplying a 9.5kw shower. Burnt out connections.
I would always install a 10mm if wirring for a new shower.

View attachment 37616

Hi - not to disagree at all with ccc etc, but this pic does look like the heat is concentrated at the termination rather than evenly along the cable. And as the neutral seems unaffected (?) it perhaps suggests in this case the cause was poor termination of the line conductor?

 

[Lee42]

Hi - not to disagree at all with ccc etc, but this pic does look like the heat is concentrated at the termination rather than evenly along the cable. And as the neutral seems unaffected (?) it perhaps suggests in this case the cause was poor termination of the line conductor?

Hi wilko. Yes that was indeed the problem.
Only been in for 8 months, so someone with plastic wrists must of installed it.
I just think it's good practice to always install a 10mm cable for a new shower install.

 

[Ian1981]

A job I'm starting a new build bungalow has been specified 16mm twin and earth for 10.5kw shower complete with a wall mounted isolation switch outside of the ensuite, which is a stud wall!
Oh the joys.

 

[Lee42]

A job I'm starting a new build bungalow has been specified 16mm twin and earth for 10.5kw shower complete with a wall mounted isolation switch outside of the ensuite, which is a stud wall!
Oh the joys.

Good luck.

Is that due to cable running through alot of insulation?
Never seen a 16mm at a shower before.
At least you can install a double 47mm metal box in the stud partition

 

[Ian1981]

Apparently 3 layers of insulation are going in so looking at reference method 101 even 16mm twin only pulls 46 amps reference method 101.
At 10.5kw I'm looking at a loading of 43-44 amps so the 16mm will be able to handle it.
I need to consult the builder and maybe request some boards are fixed above the insulation so a 10mm can be clipped above the insulation.
They won't budge to a lower rated shower tho.
Doubt I'd even manage to fit a 47mm box in the wall as the studs are only about 50mm deep

 

[Lee42]

That is a narrow stud
Thankfully always 4x2 with the joiners we work with.
Would not like to terminate a 10mm in anything less than a double 47mm box.
To be honest don't like wirring showers fullstop

 

[Lee42]

Apparently 3 layers of insulation are going in so looking at reference method 101 even 16mm twin only pulls 46 amps reference method 101.
At 10.5kw I'm looking at a loading of 43-44 amps so the 16mm will be able to handle it.
I need to consult the builder and maybe request some boards are fixed above the insulation so a 10mm can be clipped above the insulation.
They won't budge to a lower rated shower tho.
Doubt I'd even manage to fit a 47mm box in the wall as the studs are only about 50mm deep

Don't like using them, but could u fit a 47mm faster fix box to give u that extra room.

 

[Ian1981]

That is a narrow stud
Thankfully always 4x2 with the joiners we work with.
Would not like to terminate a 10mm in anything less than a double 47mm box.
To be honest don't like wirring showers fullstop

I'll get round it as I really don't want to be installing 16mm but it's not mine or my company's spec
4mm ring circuits as well.

 

[Ian1981]

Don't like using them, but could u fit a 47mm faster fix box to give u that extra room.

I've used them on 10mm never on 16mm
I can see the wall buckel as I try to push the switch back

 

[davesparks]

If it is already known that there will be that much insulation the. The electrical installation designer should first be trying to find a way to keep the cables out of it rather than plan for them to be buried in it.

 

[Darkwood]

If there is any kind of airing cupboard then a suggestion if re-routing the cable isn't an option would be a contactor operated by a lighting pull switch, cable size thus of no concern then. If the designer has issue with this then give then let them try terminate 2 x 16mm T&E into a standard shower switch and deep box.

 

[Wilko]

If the designer has issue with this then give then let them try terminate 2 x 16mm T&E into a standard shower switch and deep box.

So true DW. First one I checked was Crabtree 50A and they won't accept bigger than 10mm2.