Shower Cable

[EFLImpudence]

That is a different subject.

 

[Murdochcat]

That is a different subject.

No its not.

As the designer / installer its a very sensible precaution .................

 

[noddy997]

No its not.

As the designer / installer its a very sensible precaution .................

Absolutely correct. That needs to be taken into consideration along with the length of the cable.

 

[noddy997]

That is not correct.

A lot of flats have 10mm² as their supply cable for everything.

Not installing a product in line with manufacturer instructions would make it void from any warranty as well. But no way 6mm cable is fine for 10kw.

We're talking about electric showers that suck up a lot of power, not flats.

 

[EFLImpudence]

Rubbish.

 

[SUNRAY]

I think the only nonsense was from yourself stating 6mm is fine for a 10.5kw shower??!

You've not seen a 10.5kw shower?! Don't know where you have been then...

There are many running (incorrectly) on 4mm² and a 32A OCPD but all of that is wrong and I hope due to the incompetence of DIYers.
It is perfectly feesible that 6mm² is suitable for a 10.5KW shower, although there isn't much head room and probably none if any derating factors come into play.

During an EICR I found one of my rental properties had a replacement shower unit with the above set-up; on line calculators were happy with 6mm² with some room to spare

 

[scousespark]

The "10.5 kW" will, almost inevitably, relate to 240V, hence about 41.9A at 230V (the nominal voltage we uses for design calculations)?
The CCC of Method 6mm² cable is 47A
What's your problem with that? 41.9 is definitely less than 47.

Even if it were10.5 kW at 230V (and I've never sen a shower like that), the current would still only be about 45.7A - so, again,Method C 6mm² would be OK. - again, 45.7 is less than 47.

It certainly is. So is 4mm² (Method C CCC = 37A).
(if, as usual, it's 7.5kW at 240V, that's about 29.9A at 230V; if {very unusually} it's 7.5 kW at 230V, that's 32.60) - both 29,9 and 32.6 are less than 37.

What is that nonsense? What has 'length of run' got to do with the MCB rating?

If you're going to offer information or advice, it really ought to be correct!

Kind Regards, John

The cable is sized on the MCB rating, not the load.

 

[SUNRAY]

The cable is sized on the MCB rating, not the load.

Such as the spur on a 32A ring? We've also had regular comments stating the situation is different for heating elements as they cannot cause an overload (some of us appreciate they can )

 

[scousespark]

Such as the spur on a 32A ring? We've also had regular comments stating the situation is different for heating elements as they cannot cause an overload (some of us appreciate they can )

I don't get this. For sockets we have given designs.
The formula for the tabulated current carrying capacity is
It = In / ( Ca Cg Ci Cf )

 

[JohnW2]

The cable is sized on the MCB rating, not the load.

Indeed so, but what I've been responding to is the assertion that 6mm² cable would be inadequate "for a '10.5 kW' shower" (without any mention of the MCB rating) - but, as you say, it's also necessary that the (unmentioned) MCB rating is no greater than the CCC of the cable.

Kind Regards, John

 

[SUNRAY]

I don't get this. For sockets we have given designs.
The formula for the tabulated current carrying capacity is
It = In / ( Ca Cg Ci Cf )

You don't get that it is permitted to use a cable rated at 20A on a 32A ring or radial circuit?

 

[SUNRAY]

Indeed so, but what I've been responding to is the assertion that 6mm² cable would be inadequate "for a '10.5 kW' shower" (without any mention of the MCB rating) - but, as you say, it's also necessary that the (unmentioned) MCB rating is no greater than the CCC of the cable.

Kind Regards, John

... We've also had regular comments stating the situation is different for heating elements as they cannot cause an overload (some of us appreciate they can )

 

[JohnW2]

True. I was talking about as situation in which overload protection is actually required - and, as you say, in some situations some people will argue that the load is such that an 'overload; is 'unlikely', such that the regs only require fault protection.

I can't think of any particularly good reason why that argument cannot be used in relation to a circuit (hence cable) supplying (only) an electric shower, but I have to say that I don;'t recall having seen the argument used in that context.

Kind Regards, John

 

[EFLImpudence]

I can't think of any particularly good reason why that argument cannot be used in relation to a circuit (hence cable) supplying (only) an electric shower, but I have to say that I don;'t recall having seen the argument used in that context.

It is sometimes 'used' or done when a 45A MCB is not available (for make of CU?) and 50A is therefore (allowed to be) used.

 

[skenk]

Scousepark is correct, the circuit breaker needs to be below the ccc of the cable and higher than the design current to comply. Even in otherwise perfect conditions applying the 0.95 Cmin correction factor to 6mm cable (47A) brings the ccc to below 45amps. The next available circuit breaker is 40amps, so although ‘6mm will be fine’ it doesn’t comply.

You can however get a 9.5kw shower on a 40a mcb and 6mm cable. Being specced at 240v the 9.5kw is 39.6amps so ok on a 40a mcb (with reference method C).

The length of the run is also a factor for complying with volt drop (I make it around 35m max length to meet 5% volt drop on a 10.5kw appliance on a 6mm cable). Ignoring volt drop the next length limit will be to meet minimum fault (short circuit) current for the breaker, this could be a factor with a high Zdb/Ze and long run to the shower.