Shower Circuit

[Geffers]

Hi guys thanks to every one who contributed to my last question re- moving cable for a new board, info was well appreciated, took on board & executed. DIN rails = its the future!

Now info on the following please,

New board required with RCD protection incorperating 2 x showers & a cooker as the largest circuits.

6mm cables on all circuits doubt if i can upgrade to 10mm showers are 9kw each so-

will 45a breakers do the showers & 40 for the cooker & can i run all 3 of them through 1 x 80a RCDas protection for these circuits only?

It will be a split load board with 63a rcd covering the rest of the circuits.

Guinness

 

[revjames]

9kw shower = 39.1A.... depending on ref method and how you derate it for insulation etc its going to be close on 6mm

OSG table 6E1

6mm ref method B (conduit/ trunking in a wall) best you are going to get is 38A and thats before you apply volt drop calc for distance.....

But what do I know I'm just a vicar with an on site guide

 

[steptoe]

I wouldnt even contemplate 45A on a 6mm cable,

and 40 only in very extreme circumstances,

not only on the de-rating side, but have you tried VD ?

I would say, as a first answer,

its never going to happen,

but you need to do some very serious calcs if you are contemplating this,

personally, I cant see you getting the figures you need, :|

---------- Post Auto-Merged at 18:47 ---------- Previous post was made at 18:45 ----------

But what do I know I'm just a vicar with a guide

but what a guide,!!!

 

[Evans Electric]

9kw shower = 39.1A.... depending on ref method and how you derate it for insulation etc its going to be close on 6mm OSG table 6E1

6mm ref method B (conduit/ trunking in a wall) best you are going to get is 38A and thats before you apply volt drop calc for distance.....

But what do I know I'm just a vicar with an on site guide

Never mind.....could have been a Vet without a guide :innocent

 

[Hefferl]

Hi guys thanks to every one who contributed to my last question re- moving cable for a new board, info was well appreciated, took on board & executed. DIN rails = its the future! Now info on the following please,

New board required with RCD protection incorperating 2 x showers & a cooker as the largest circuits.

6mm cables on all circuits doubt if i can upgrade to 10mm showers are 9kw each so-

will 45a breakers do the showers & 40 for the cooker & can i run all 3 of them through 1 x 80a RCDas protection for these circuits only?

It will be a split load board with 63a rcd covering the rest of the circuits.

If you divide the circuits in this manner then a trip of the 63A RCD will leave the premises with no lights from either the lighting circuit(s) or any lamps which maybe plugged into socket outlets

 

[jameseye12]

If you divide the circuits in this manner then a trip of the 63A RCD will leave the premises with no lights from either the lighting circuit(s) or any lamps which maybe plugged into socket outlets

Agreed. Division of the board will leave the property with virtually no power. What good will the showers and cooker do when the toaster explodes and takes out the RCD? This contravenes reg 531.2.4

 

[steptoe]

guys, I think you are missing the important thing here,

inconvenience is only a recommendation,

overloading is something more serious.

 

[kerching]

But what do I know I'm just a vicar with an on site guide

first it was BRB, then BGB.....all along RevJames has had the BBB [King James Ammendment I]

 

[Hefferl]

guys, I think you are missing the important thing here,inconvenience is only a recommendation,

overloading is something more serious.

Agreed indeed it is more serious but not missing the point at all Steps - the OP posed three questions

(1) Cable current carrying capacity

(2) Selection of protective devices

(3) Distribution of circuits across RCDs

Points (1) & (2) where addressed by posts #2 & #3 but nobody had answered point (3) which is why I reponded.

 

[steptoe]

point taken Hef,

but I think ,IMO, that we can stop before we reach the segregation stage as of this present time we wont get there,

like failing on a dead test, you dont continue on to the live part.

step (1) is not likely to be passed,

so all other steps are pretty much academic really.

 

[Hefferl]

Just trying to help

 

[mikep]

I would use a high integrity CU pop a couple of RCBO's one for each shower on the front end after main isolator then run the split load as normal for all other circuits, and calc the runs for the shower cables.

or split tails with henley with separate shower CU's

 

[Geffers]

Nice one guys i knew you wouldn,t let me, down gonna push for an increase in cable size & go with RCBOs for showers -or leave it & walk away.

 

[Geffers]

FYI I left it not worth the hassle or the risk, Customer Refused my suggestion to upgrade the cable.

 

[kme]

Then they`re asking for trouble - watch for the guy with the horse arriving..............

I`d also be quizzing the size of the DNO supply - if its a 60 or 80; its woefully inadequate. I don`t even like 2 9KW showers, when cooking is gas; let alone with a cooker stuffed in the mix.

 

[ProDave]

yes, unfortunately walking away, will just mean they will keep asking until they find somebody who will do it with the existing cables, as noted, complete with his horse.

My approach would have been try and persuade them to fit only 8KW showers, then you might (and it's still a might) be able to squeek within limits and use the 6mm cable.

For what it's worth, I have 2 8KW showers (on 10mm cable and 40A MCB's) and have not had any issues running both together, max current measures no more than 70A

 

[S60TEM]

Customers sometimes hack me right off!

As said above CCC for 6mm......NEVER put on a 45A breaker and unless its a really short run, never a 40A either as anything above 225v will give you in excess of 40A.

I always advise customers that want new build extensions etc with new kitchen circuits and upstairs shower rooms etc to contact DNO for a check on their OPD as they're mainly always 60/80A so I reccomend they get them changed to 100A. Some customers listen and appreciate the depth of thought and explanation as to why and others just think i'm trying to up my price for no reason and they are the jobs that I either don't get or I refuse.

 

[revjames]

Customers sometimes hack me right off!As said above CCC for 6mm......NEVER put on a 45A breaker and unless its a really short run, never a 40A either as anything below 225v will give you in excess of 40A.

.

 

[andy_spark]

As a side issue who has enough water pressure to run 2 mains fed electric showers at the same time? (Apologies now if they are pumped from a header tank as that is a different issue.) Regardless of how they are protected and cabled are both showers going to be used together? In my house some only has to fill the kettle and it messes the shower up.

Also what sort of cooker will be drawing 40Amps? Diversity calculations give about 26Amps for a cooker circuit, including a 13A socket on the Isolator and unless it is christmas day that is never likely to be acheived. I see no reason why a 40A shower and a 32A cooker can not go on the same side of a 63A rcd.

Also I have been lucky enough to obtain some 6mm Low smoke cable left over from a job, this has been ideal for some profitable shower installs bearing in mind it can carry up to 58Amps clipped direct, and 51A in trunking.

 

[ProDave]

As a side issue who has enough water pressure to run 2 mains fed electric showers at the same time? (Apologies now if they are pumped from a header tank as that is a different issue.) Regardless of how they are protected and cabled are both showers going to be used together? In my house some only has to fill the kettle and it messes the shower up.

We do, our 2 electric showers are quite often used together (B&B) In fact on at least one occasion the third one was in use as well (our own shower is a mixer shower taking hot and cold from the mains pressure water tank, partly because 3 electric showers would be too much, and partly because electric showers are useless and we wanted something better)

Also what sort of cooker will be drawing 40Amps? Diversity calculations give about 26Amps for a cooker circuit, including a 13A socket on the Isolator and unless it is christmas day that is never likely to be acheived. I see no reason why a 40A shower and a 32A cooker can not go on the same side of a 63A rcd.

I had to investigate tripping of an all electric range cooker. The total rated load was something like 16KVA. It was fed with a long run of 6mm t&e It had something like 5 electric rings, a hotplate, 2 ovens and a grill.

Customer refused my quote to increase cable size to 10mm so I could fit a larger MCB, so I just left it as it was, with the customer regularly having to reset the MCB when too many things were in use together.