Strange Shower Setup

[securespark]

 

[Spark123]

Yeah, a little bit odd in the respect that the MCB is on its own. If the RCD and the MCB were in the same enclosure utiliting the RCD as the main switch we wouldn't look twice, I take it the RCD also feeds more consumer units?

 

[securespark]

The meter tails feed a stand-alone RCD. The outgoing line/neutral feed a Wylex standard unit out of shot.

The MCB you see is fed from the outgoing line terminal of the RCD and the outgoing terminal of the MCB is then taken into the Wylex standard unit and connected up to the line conductor of a twin & earth cable. The neutral and cpc of the T&E are connected to their respective terminals in the Wylex CU.

If the spark was going to go to all the trouble to fit a separate enclosure for the MCB, they might as well have gone for a conventional CU arrangement...

 

[Spark123]

Oh
So turning off the main switch on the wylex CU should be shower be in use causes a feedback through the neutrals and makes it all live

 

[securespark]

 

[securespark]

The implications?

How would you code it?

 

[Spark123]

Code 1. It is dangerous as it renders the board isolator useless, can cause 240v to be aparrent on the neutrals with the isolator open should the shower isolator be closed.

What size is the isolator, I'm just thinking why it has been done this way - possibly a 60A CU so couldn't fit a 40A MCB in it? But they used the neutral rail in the CU anyway.

 

[securespark]

The CU, cut-out fuse & stand-alone RCD are all rated 60A.

Don't quite follow what you're saying about the shower iso being closed?

 

[Spark123]

I take it the shower has a pullcord isolator etc? Maybe clearer if I just said switch it on.

A little scenario, someone is wanting to change a lamp fitting so they come along and remove the fuse for it and turn off the isolator on the CU. They start work, prove all is dead etc no problems.

Someone comes along 5 minutes later and wants a shower, switches the shower on as normal, but nothing happens (as the neutral is open ckt). In doing this completes the circuit and now there is 240v on the neutral bar in the CU and the poor bloke changing the lamp fitting gets a belt.

What size MCB, what size shower, what else is on the CU etc?

 

[RF Lighting]

Don't quite follow what you're saying about the shower iso being closed?

I know he's a big lad and is quite capable of speaking for himself, but I thing the point Spark123 is trying to make, is that if the main switch in the wylex CU is 'off', and the local DP shower isolator is 'on', then this will cause neutral feedback through the shower unit making all the installation neutrals rise to mains potential.

If the local DP isolator was 'off' then there would be no neutral feedback.

Definatly a code 1 from me aswell. I take it the live for the shower circuit is single insulated in that picture aswell?

 

[Spark123]

You explain it better than me rob

 

[securespark]

No, I've got the principle of what you're saying, guys!

But, Rob, wouldn't the shower have to be running to make the circuit, as numerical suggests?

The cables are single insulated, yes. And where it enters the metalclad CU, there's no grommet.

 

[RF Lighting]

But, Rob, wouldn't the shower have to be running to make the circuit, as numerical suggests?

A neon in the switch or a power light on the shower should be sufficent.

Maybe not a fatal shock, but still unpleasant

 

[Spark123]

The shower doesn't need to be running, just switched on to complete the circuit. The heater element will be enough to cause the neutral potential to rise. The only saving grace may be the whole installation is RCD protected (30mA?).

 

[securespark]

Gotcha!

Let's say the circuit has been really badly installed & there is no iso, or just one without a neon. Then the circuit would not be closed. And if you had a shower that needed juice to start up, then there would be no danger I guess.