Shower and cooker circuits

[MrGwythers]

Hello I'm an apprentice but don't do any domestic work just commercial and industrial atm.
My question is if you don't have a design current for shower or cooker e.g. customer doesn't know what they are buying yet, how do you select your cable sizes and mcb rating?
This is purely for learning purposes.

 

[Andy78]

Hello I'm an apprentice but don't do any domestic work just commercial and industrial atm.
My question is if you don't have a design current for shower or cooker e.g. customer doesn't know what they are buying yet, how do you select your cable sizes and mcb rating?
This is purely for learning purposes.

You would get the customer to pull their finger out, choose the product, and give you a design current.

 

[Harry_P]

Hello I'm an apprentice but don't do any domestic work just commercial and industrial atm.
My question is if you don't have a design current for shower or cooker e.g. customer doesn't know what they are buying yet, how do you select your cable sizes and mcb rating?
This is purely for learning purposes.

Hi there is no way you can select the cable until you know what the design current is (Ib)
The design current will let you be able to select the appropriate protective device with the appropriate current rating (In)
Then you can select your suitably rated cable (Iz)
Ib<In<Iz

 

[Midwest]

Hi there is no way you can select the cable until you know what the design current is (Ib)
The design current will let you be able to select the appropriate protective device with the appropriate current rating (In)
Then you can select your suitably rated cable (Iz)
Ib<In<Iz

That would pose a problem for most new builds, where appliances aren't included in the spec.

I would suggest 32A supply for a fixed cooking appliance, and a 45A supply for an electric shower (although if its a shower, they are normally supplied & installed).

 

[Harry_P]

That would pose a problem for most new builds, where appliances aren't included in the spec.

I would suggest 32A supply for a fixed cooking appliance, and a 45A supply for an electric shower (although if its a shower, they are normally supplied & installed).

I'm not sure why you think there would be a problem for new builds? New builds will have standard circuits installed where the load capacity is known I.e 32 amp rfc and 6 amp lighting circuits. This is a single circuit that is being designed and installed after the property has been built hence Ib<In<Iz is the formula used to select the appropriate equipment

 

[littlespark]

Future proof it and wire it in 10mm. The mcb can be decided when the shower size has been found out.

Or

Wire it in 6mm, taking wiring methods and length of circuit into account and tell customer he’s limited to a smaller size.

Basically the load has to be known before the circuit can be designed

 

[Taylortwocities]

I agree with littlespark

Future proof it and wire it in 10mm.

And tell them the maximum demand for both the shower and the "cooker".

Note that cooker implies a device that includes one (or more) ovens and a hob.
This could end up being separates (induction hob and a separate double oven), or it could be a stonking great range cooker.
Installing 6mm and a 32A MCb would limit the choice, and there's very little material cost between 6mm and 10mm cable.

 

[Midwest]

I'm not sure why you think there would be a problem for new builds? New builds will have standard circuits installed where the load capacity is known I.e 32 amp rfc and 6 amp lighting circuits. This is a single circuit that is being designed and installed after the property has been built hence Ib<In<Iz is the formula used to select the appropriate equipment

New builds design their cooker circuits without any knowledge of what the customer intends to install in their property.

Fortunately, most domestic cooking appliances, the 'vanilla flavoured/essentials' ones would only ever need a 32A supply. I don't use the formulae per say, just ask what the customer is having. Most would be happy on a 32A.

 

[FatAlan]

I understood what you were getting at Midwest

 

[Harry_P]

New builds design their cooker circuits without any knowledge of what the customer intends to install in their property.

Fortunately, most domestic cooking appliances, the 'vanilla flavoured/essentials' ones would only ever need a 32A supply. I don't use the formulae per say, just ask what the customer is having. Most would be happy on a 32A.

It all depends on what kind of work you do I suppose, if you only ever install small white goods then you will usually be ok with the standard circuits, if you have got to install a range cooker and an induction hob then standard circuits may not be appropriate and you start to earn your money as an electrician by designing as well as installing the accessories.

 

[Midwest]

 

[Midwest]

We had a RangeMaster Range cooker in our old place. Hobs were gas, but electric main oven, grill & side oven. Can't remember the max load, but it was around 8kW.

Was connected up by their engineer, who insisted it needed 40A supply.

I subsequently clamped it, and could never get above 12A with all guns blazing. Lovely cooker. We do miss her.

I also connected up an all electric version, for a customer. It again had been installed by one of their engineers, this time to a 32A supply. I queried this with their tech support, as the manual suggested 40A supply, who confirmed it needed 40A. Which was a conundrum, as the customer only had a 32A available, so we left it on the original 32A, and never an issue.

My point is, unless its several different devices, or in a commercial setting, a 32A supply is all thats often needed, applying diversity of course.

 

[MrGwythers]

So for a cooker a 10mm would be fine for a maximum rated cooker possible, so would you just use a 32a mcb and then if need be up the rating of the mcb.

Same with shower circuit use a 10mm and a 32/40a mcb obviously by time it came to installing the appliances you should have the information needed.

 

[Andy78]

So for a cooker a 10mm would be fine for a maximum rated cooker possible, so would you just use a 32a mcb and then if need be up the rating of the mcb.

Same with shower circuit use a 10mm and a 32/40a mcb obviously by time it came to installing the appliances you should have the information needed.

If you like wasting money and working/struggling with oversized cables then this would be a way forward.

 

[Taylortwocities]

So for a cooker a 10mm would be fine for a maximum rated cooker possible, so would you just use a 32a mcb and then if need be up the rating of the mcb.

The rating of the MCB is chosen as being appropriate for the fixed wiring, not the rating of the cooker.
Unless the MI dictates a specific size of fuse, etc..

 

[MrGwythers]

The rating of the MCB is chosen as being appropriate for the fixed wiring, not the rating of the cooker.
Unless the MI dictates a specific size of fuse, etc..

How do you mean? I thought it was more mcb rating for the appliance Depending on power, cable sizes depending on rated mcb e.g current carrying capacity higher than rated mcb ?

 

[MrGwythers]

The rating of the MCB is chosen as being appropriate for the fixed wiring, not the rating of the cooker.
Unless the MI dictates a specific size of fuse, etc..

How do you mean? I thought it was more mcb rating for the appliance Depending on power, cable sizes depending on rated mcb e.g current carrying capacity higher than rated mcb ?

 

[FatAlan]

MCB is there to stop the cable from frying should the current exceed its capacity. As hinted at above.