shower priority unit positioning

[toadman]

hi everyone, I'm in the process of converting an outbuilding into a granny annex which will have an electric shower installed I've been told I'll need a shower priority unit positioned in the main house next to the cu which will then feed the annex shower directly without need to involve the cu in the annex, what armoured cable will I need to supply both the annex cu for all the other circuits and shower independently , thanks

 

[MJPD29]

Your electrician should be more than capable of calculating that for you, if not then he shouldn't be doing the job.

 

[toadman]

thanks for the relays, a great help

 

[MJPD29]

thanks for the relays, a great help

If your doing this yourself you should be capable of calculating it, if you can't then you shouldn't be doing it.

 

[davesparks]

hi everyone, I'm in the process of converting an outbuilding into a granny annex which will have an electric shower installed I've been told I'll need a shower priority unit positioned in the main house next to the cu which will then feed the annex shower directly without need to involve the cu in the annex, what armoured cable will I need to supply both the annex cu for all the other circuits and shower independently , thanks

Why do you need a priority unit? Have you looked at other hot water solutions instead of electric showers?

As far as cable size and type goes you haven't given us anywhere near enough information to even give a rough estimate.

We need to know information such as what the electrical load will be on each circuit, circuit length, nature of the route, how it will be installed.
We would also need to know what type of incoming supply you have, what the earthing system is and what the earth fault loop impedance/prospective fault currents are.

 

[mainline]

hi everyone, I'm in the process of converting an outbuilding into a granny annex which will have an electric shower installed I've been told I'll need a shower priority unit positioned in the main house next to the cu which will then feed the annex shower directly without need to involve the cu in the annex, what armoured cable will I need to supply both the annex cu for all the other circuits and shower independently , thanks

The point of a priority unit is so that you can't use 2 showers at the same time, and one of them will have a priority over the other (Basically a contactor).

Being told you need one is suggesting that you may not have the capacity.

More info would be helpful.

 

[toadman]

I'm doing most of the work myself including putting in an armoured 16mm cable which is about a 30 m run and will get everything signed off when completed i understand why I need the priority unit , there's 9kw shower going in the annex and the main fuse won't support 2 showers, my question is can I run an 16mm 5 core cable to supply both shower directly and annex cu, the other circuits at lights 6amp sockets 32amp cooker 32amp smoke alarm 6amp



























,

 

[nicebutdim]

Why are you using 16mm cable?

 

[toadman]

I was told that would be the way to go

 

[nicebutdim]

I was told that would be the way to go

I've no idea about the installation conditions, but 16mm seemed unusual for the stated load. There may be valid reasons for using this size, but none that immediately jump out at me.

The use of 5 core cable for 2 circuits isn't particularly unusual, provided ADS is satisfied.

 

[DPG]

You really need to be speaking to the electrician who will be testing and signing it off. Otherwise you risk doing the work and then it not getting signed off and certified.

 

[toadman]

I've no idea about the installation conditions, but 16mm seemed unusual for the stated load. There may be valid reasons for using this size, but none that immediately jump out at me.

The use of 5 core cable for 2 circuits isn't particularly unusual, provided ADS is satisfied.

I've no idea about the installation conditions, but 16mm seemed unusual for the stated load. There may be valid reasons for using this size, but none that immediately jump out at me.

The use of 5 core cable for 2 circuits isn't particularly unusual, provided ADS is satisfied.

do you think 10mm would work?

 

[DPG]

do you think 10mm would work?

It depends on various factors including installation conditions. Volt drop calculations also need doing.

 

[Gurnatronics]

I’m assuming greater than 10mm ie 16mm as they are exporting the PME and using it to bond the water pipes?

 

[Midwest]

Have you actually found out how you will get this additional work 'signed off'. It sounds like this is part of some building work, that may be under planning or a building notice? Have you spoken to your LBC about this?

 

[MJPD29]

do you think 10mm would work?

How did you calculate that you would need 16mm? If 16mm is the figure that was calculated to be required, then no 10mm would not work.

 

[Spoon]

Why are you using 16mm cable?

I was told that would be the way to go

Welcome to the forum mate.
Who told you?
Why are you not discussing this with the electrician who will be signing off the work? They may want it installed in a particular way.

 

[davesparks]

I'm doing most of the work myself including putting in an armoured 16mm cable which is about a 30 m run and will get everything signed off when completed i understand why I need the priority unit , there's 9kw shower going in the annex and the main fuse won't support 2 showers, my question is can I run an 16mm 5 core cable to supply both shower directly and annex cu, the other circuits at lights 6amp sockets 32amp cooker 32amp smoke alarm 6amp

If the main fuse won't support 2 showers will it support 1 shower and 2 cookers?


Whilst a single multicore cable can be used for multiple circuits this would usually only be done when those circuits are terminating in the same place. In this case you would need to joint the 5 core cable onto 2 other cable, one to go to the CU and one to go to the shower, this just adds an unnecessary and ugly joint to the installation.

Also why would you use 5 core SWA for 2 circuits?

 

[mainline]

do you think 10mm would work?

I would use the 16mm 5 core.
What's the earthing system ?
Has the annex any extraneous conductive parts ?

 

[mainline]

If the main fuse won't support 2 showers will it support 1 shower and 2 cookers?


Whilst a single multicore cable can be used for multiple circuits this would usually only be done when those circuits are terminating in the same place. In this case you would need to joint the 5 core cable onto 2 other cable, one to go to the CU and one to go to the shower, this just adds an unnecessary and ugly joint to the installation.

Also why would you use 5 core SWA for 2 circuits?

He could take the 5 core to one CU and feed the shower from there.

 

[davesparks]

He could take the 5 core to one CU and feed the shower from there.

It would be bad practice to have a circuit in the CU which is not isolated by the mainswitch of the CU.

 

[mainline]

It would be bad practice to have a circuit in the CU which is not isolated by the mainswitch of the CU.

Use a contactor or a 3 pole main switch

 

[nicebutdim]

do you think 10mm would work?

I've no idea what would work, for reasons previously outlined and others had already made the same point.

If you correctly guess how long the piece of string sitting in my cupboard is, I'll take a wild guess at answering your question.

 

[davesparks]

Use a contactor or a 3 pole main switch

I don't see how that will help.

 

[mainline]

I don't see how that will help.

Using a 3 pole mains switch would isolate all circuits.

Using a contactor would isolate the outgoing shower circuit.

Using a CT relay at the House would mean you could also limit other circuits if there was lack of capacity.

 

[James]

Using a 3 pole mains switch would isolate all circuits.

Using a contactor would isolate the outgoing shower circuit.

Using a CT relay at the House would mean you could also limit other circuits if there was lack of capacity.

a contactor will normally turn off a circuit but i would not consider it isolated.
not trying to be pedantic but we should use the correct terms for things as professionals so that we leave nothing to the imagination or interpretation of our words.
unless of course you think a contactor is a suitable means of isolation and then i would just call you out as Wrong.

 

[mainline]

a contactor will normally turn off a circuit but i would not consider it isolated.

Why not ?

not trying to be pedantic but we should use the correct terms for things as professionals so that we leave nothing to the imagination or interpretation of our words.

What term did I use that was wrong ?

unless of course you think a contactor is a suitable means of isolation and then i would just call you out as Wrong.

Table 537.4 60947 contactor isolation = yes

 

[mainline]

James said:
unless of course you think a contactor is a suitable means of isolation and then i would just call you out as Wrong.



No more debate ?

 

[Midwest]

Ok.

I'm thinking a contactor has a control circuit, which would operate said contactor. Whereby you could isolate the control circuit. But does that safely isolate the circuit, like a standard isolator would do. What does BS7671 say about isolation?

 

[mainline]

Ok.

I'm thinking a contactor has a control circuit, which would operate said contactor. Whereby you could isolate the control circuit. But does that safely isolate the circuit, like a standard isolator would do. What does BS7671 say about isolation?

Bs7671 gives guidance on what can be used for Isolation, emergency switching and functional switching.

Table 537.4 60947 contactor isolation = yes

 

[James]

I have not got time to look in depth into it.
however my thoughts, right or possibly wrong as you have pointed out.

An isolator is a means of removing power from a circuit to allow amongst other things, work to be safely carried out on it.
a contactor by its very nature may bring power back to the circuit if it receives power to the coil, this may be from an automatic device like a thermostat or a remote switch.
I for one, would only rely on a contactor for isolation of a circuit i was working on under some very specific circumstances. and also, I have yet to see a contactor that has a means of locking off.

 

[nicebutdim]

Maybe not the wisest place for this discussion.

 

[James]

yes, @nicebutdim I hadn't considered that.
perhaps if anyone wants to discuss it further then a new thread would be better.