Upgrade 7kw Shower to 8.5kw Shower - New Fuse Needed?

[fuzzball]

Hi
I have searched for this and am even though it appears to be a common question I am still confused so...

I am upgrading a 7kw shower to a 8.5kw shower. My wring is 6mm and I don't want to upgrade to 10mm.

1. I believe my wiring is suitable for 8.5kw but would like confirmation.

2. Do I need to upgrade my fuse?

Thanks

 

[Lectrician]

Depends hugely on how the cable is installed, how long the run is etc etc. This is why it is not a cut and dry question.

 

[fuzzball]

I think these are the answers. The house was built in 1992, and is a 4 bed detached, if that helps.
The cable goes from the bathroom up into the loft, then under the loft insulation and down between the walls to the mains.
The fuse box is in the garage directly beneath the bathroom so I assume the run is not that long.

Does that help to give an answer or have I just made myself look more stupid?

 

[davy_owen_88]

6mm² cable under >100mm of loft insulation has a CCC of 27A.
8.5kW @ 240V = 35.4A.

If you can get up the loft and pull the cable from under the insulation and clip it to the joists where they will not be covered with insulation then your cable will carry the load of an 8.5kW shower no problem.

Whether you need to upgrade your fuse depends on what fuse you currently have...

Does your consumer unit contain an RCD? Most shower manufacturers insist on RCD protection so this will need to be considered.

 

[fuzzball]

Hi
Sorry but I can't find what I am sure is basic information on this.
I have spent the last hour searching but can't find a basic guide to this stuff.
1. Can you tel me what CCC is and why it makes a difference to the CCC value whether the cable is under insulation or not.
2. Have I understood correctly what an RCD is. The fusebox has it's own independent switch for each shower to break the circuit. Is this the RCD you mention.
Over what I believe is the RCD on the fusebox it says it is a 32 Amp Fuse.
Does this make any difference to what I can/can't do to upgrade from 7kw to 8.5kw.

Thanks and sorry if this is all a bit basic for you guys

 

[davy_owen_88]

CCC = current carrying capacity

Every cable has a CCC and this is determined by the maximum temperature the conductor and it's insulation can safely 'work' at. If you take a certain cable and run it in free air it can carry more current than if it was under insulation because the heat generated can be dissipated more easily.

RCD = residual current device.

This device monitors the current flowing 'in' through the phase conductor and compares it to the current flowing 'out' through the neutral. If there is an imbalance then current is going somewhere it shouldn't (through you for example) and the RCD trips. What you think is an RCD is actually an MCB (minature circuit breaker) This detects over current situations due to overload or fault currents.

For an 8.5kW shower you will need to upgrade your 32A MCB to a 40A MCB. You can only do this safely if you move the cable from under the insulation and clip it to the joists - the joist will act as a heatsink and allow the heat to be dissipated more easily.

 

[Lectrician]

A loft can also be prone to higher than normal ambient temperatures, and this should also be taken into account. This is why it has become the norm to say "fit 10mm" - and even then, you would find that possibly 16mm would be called for on some installations, which is mad when you consider that you have 16mm feeding your house.....but not mad if you understand the calculations that go behind selected the correct size.

 

[fuzzball]

Thanks For The Help.

One last idiot question. Is there a technique to get the MCBs to just pop/pull out or do I have to unscrew the face panel of the unit whole unit to get at them to do the upgrade. The brand name is QWIKLINE.

Again, apologies for the low level of question.

 

[Steve]

Thanks For The Help.

One last idiot question. Is there a technique to get the MCBs to just pop/pull out or do I have to unscrew the face panel of the unit whole unit to get at them to do the upgrade. The brand name is QWIKLINE.

Again, apologies for the low level of question.

turn off main switch, unscrew face panel (beware incoming wires still live) and unscrew MCB top and bottom.

 

[securespark]

Each shower........

How many have you got??