Shower Issue

[Englishman]

Went to a job today as a follow on from another sparks on our firm. Was a "fishy smell" reported, and was advised that the cable was undersized.

Get there today and find a 6mm cable, 40a MCB and 9.5kw shower; and this in the isolater...

Now, the supply voltage is 242, the cable run goes from the board, up to the first floor in a piece of conduit in the wall (reference method A) which rates at 34a, and then up a void behind the shower, clipped direct (reference method which rates the cable at 47a.

Obviously the cable at the lowest part (bit going through conduit) is carrying 39.25a; which is greater than 34a, and they're sending me back to put a 10mm supply in tomorrow. My argument is that the damage to the cable has been caused by a loose neutral at the isolater and that although the cable is undersized, it's not massively bad and probably wouldn't cause a huge amount of issues if the shower was run normally.

Opinions please boys....

 

[davesparks]

Is the conduit buried in an insulated wall? If not I can't see where the lower rating has come from. Method C rating according to BGB is 47A.
If it's in the wall or buried in a normal masonry wall then would it not be method C?

 

[Englishman]

I was going worst case scenario.

The wall that the conduit is in, is made of hollow bricks.0

 

[davesparks]

Not an insulated wall then, that's a masonry wall, albeit one with a draught running up it!

 

[Englishman]

True, bit nothing in the bgb about conduit in masonry (hollow pain in the arse) walls!

 

[davesparks]

Isn't there? Consider installation methods 58 and 60, look up the relevant tables and make an informed decision.
There isn't a rating for t&e in conduit in a masonry wall but there is one for it in capping/oval conduit and another for 70degree sheathed cables so use that info to aid you in deciding what rating is appropriate.
Not forgetting the BGB is not gospel but a non-statutory British standard.

 

[Englishman]

So we're looking at B for the conduit run and C for the rest. 41a and 47a, shower will pull 39.25a at it's maximum.

 

[Hawk]

How long is the run of cable?

 

[Englishman]

About 5 metres

 

[Hawk]

Borderline 6mm. If it was me I would have used 10mm. Future proof aswell.

 

[Geordie Spark]

I know it's the loose neutral which has caused the issue that I responded to.

What I'm referring to the forum is how much it actually needs to be changed. And how much of an issue would be caused by leaving it.

Peronally I would be replacing the isolator and keeping the cable as it is BUT when the Gaffer tells you to go back and change the cable then that's what you do!!

REMEMBER; the gaffer may not always be right, but he is ALWAYS the gaffer!!

Just nod, smile and do what he says no matter how stupid it is as long as it isn't dangerous,

 

[Englishman]

Just to reiterate, it wasn't me who installed the cable, much as I despise working with it, I always use 10mm, this was a job I went to.

Was told to change it by my team leader yesterday, spoke to our QS and my boss this morning and explained the situation, and they agreed that it didn't need changing. Just went and checked everything again today, filled out a minor works cert for the replacement of the isolator and explained the situation to the tenants.

The first spark that went didn't even check anything, just looked at the shower rating, cable size, and condemned it to the tenant. Just left the cable to burn.

 

[Hawk]

Did you try putting a clamp meter on it to see what current the shower was pulling on full power?

 

[shanky887614]

I would say it might not be a loose neutral connection. The other possibility is the pull cord itself is at fault. I have replaced 4 GET 45amp pullcords in this last week. All looked identical to that in the picture. I do a lot of maintenance for an estate agent and the most of the calls I get are showers and 9/10 its the pullcord. Try a different make as well as insuring all terminations are tight.

what brand do you use? we tend to use 45amp crabtree pullcords.

the only problem we have had is from time to time it doesnt always click properly but a quick swap and crises averted

 

[Englishman]

Did you try putting a clamp meter on it to see what current the shower was pulling on full power?

No, because I don't routinely carry one on the van tbh, but, Ohms law stipulates that it couldn't pull any more than 39.25a anyway.

 

[davesparks]

what brand do you use? we tend to use 45amp crabtree pullcords.

the only problem we have had is from time to time it doesnt always click properly but a quick swap and crises averted

Considering he said GET 45amp pullcords i'd hazard a guess at the brand being GET