Electrical wiring queries (2...so far!)

[jim]

Do these sound right & proper?

a) 2 X 16A immersion heaters in a heatbank

Both on one circuit on a 32A MCB, on a new 2X RCD split CU. Seperately switched, in two locations viz:- 1) next to heatbank via 2 X switched fused spurs (?) with a 13A (plug type) fuse in each 2) in neighbouring room via 2 X 45a DP switches (more convenient for residents to control)

Queries

13A fuses for 16A immersions? 45A DP switches - wouldn=92t 20A DP do and be a bit cheaper?

b) Is it a requirement (or worth doing) to cover cables on walls with plastic capping prior to dot=92n=92dab plasterboarding and skimming? If it=92s been installed is there any way of checking apart from destructive investigations?

cheers

JimK

[ARWadsworth]

a) 2 X 16A immersion heaters in a heatbank

Both on one circuit on a 32A MCB, on a new 2X RCD split CU. Seperately switched, in two locations viz:-

1) next to heatbank via 2 X switched fused spurs (?) with a 13A (plug type) fuse in each 2) in neighbouring room via 2 X 45a DP switches (more convenient for residents to control)

Queries

13A fuses for 16A immersions? 45A DP switches - wouldn?t 20A DP do and be a bit cheaper?

b) Is it a requirement (or worth doing) to cover cables on walls with plastic capping prior to dot?n?dab plasterboarding and skimming? If it?s been installed is there any way of checking apart from destructive investigations?

I would expect two 16A MCBs and two 20A DP switches.

There is no requirement for capping.

Adam

[Harry Bloomfield]

The 13amp fuses might well last for months, but none the less they are not appropriate, nor is the spur unit rated at 16amp.

Two separate circuits from the DB would be a better way to it, each rated at 16 or 20amp. Failing that, a 2way DB mounted at the far end of the 32amp feed, with a 20amp rated DP switch for control.

[Dave Plowman (News)]

Are they actually 16 amp? Common ones are 3kW so 13 amp fusing is fine. But are normally fed with a 16 amp radial circuit from the CU as that's the closest MCB - and the circuit will be protected ok by that.

Indeed. Perhaps they had a job lot. ;-)

[ARWadsworth]

the heaters consists of. I do like the idea of a 2 way CU at the far end of the circuit if it is a 4mm or 6mm supply.

Adam

[jim]

yep I'll have a look later on and come back with full spec. cheers JimK

[jim]

ok had a look now and there is

both wired to 1way in the CU (tho outside of the RCDs so presumably it's a 32A RCBO? - has a yellow test button) from CU in 2 runs of 4.0mm T+E to the 45A DP switches, from 45A switches in 2 runs of 4.0mm T+E to the 13A switched fused spurs next to the heatbank from the 13 A spurs in heat resistant 3 core flex to each immersion

yes the immersions are 3kw each (the install notes required 16A supplies for each which was where I got the 16A idea from...)

JimK

[John Rumm]

In which case that all seems to be in order then ;-)

[jim]

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cheers to all JimK

[ARWadsworth]

It is just an odd setup. I cannot find anything dangerous about the setup it just seems odd or just overkill. The sparks may not have had the specs about the heaters. He certainly did not lay 4mm T&E for fun.

The standard circuit would be two seperate 16A MCBs using 2.5 T&E and 20A double pole switches in all rooms.

As John says, "it is in order"

Adam

[jim]

ge

As I recall the heatbank was there when they wired it up (so heaters specs etc were freely on view to them).. The 12 way CU is very full though perhaps that may be why - to leave a couple of spare ways?

JimK

[Tim S]

jim coughed up some electrons that declared:

It's not illogical.

For my heatbank, I've allowed a single 45A RCBO in the main CU.

That will feed a local set of MCBs at the heatbank cupboard, 3 x 16A for the

3 immersion heaters and 1x 6A for the control circuits and boiler.

It made more sense than 4 x RCBOs or 1 x RCD + 4 x MCBs in the main CU (which is large and still fairly full).

It also makes sense (to me at least) to be able to throw the 45A RCBO and know that the entire heating system is dead.

It also allows me to house the 16A MCBs alongside contactors to operate the immersion heaters from the main tank stat via a changeover switch where the switch selects gas boiler or electrical backup driven by the same initial control (tank stats and possibly a timer).

Cheers

Tim