Connect Underfloor Heating from Shower Swicth

[billau]

I've read the debates about running a spur from the power supply to a shower but still need some help. My shower is connected directly to the fuseboard and a 32a MCB and 10mm t&e cable, When first installed it was an electric shower but we since replaced it with a power shower so it presumably draws a lot less power.

I would like to connect my underfloor heating (warmup) - 400 watts, 1.7amp using 2.5mm t&e. The most convenient connection is the switch for the shower. Given that the shower is now a power shower would this be OK, and would I need to fit a lower rated MCB?

 

[ColJack]

you would need to connect the 10mm to a fused spur and run the heating off of that, fused down to 3A...

this work is notifiable under Part P of the building regulations as it's a "special installation" in a "special location"..

 

[billau]

Sorry, you mean break into the 10mm cable and insert a fused spur, then run 2.5mm from that?

 

[ColJack]

you shouldn't be running anything in 2.5 from a 32A breaker..

your best bet, given the LABC notice you will have to give and pay for if you do it yourself, is to get a registered electrician in to do the work..

he'll do it quicker and do it properly rather than just lash it onto the end of any spare cable that happens to pass by..

 

[stem]

My shower is connected directly to the fuseboard and a 32a MCB and 10mm t&e cable.........we since replaced it with a power shower so it presumably draws a lot less power.

Hope you've downrated it to 3A somewhere and don't have an appliance taking about 2A connected directly to a 32A MCB

 

[billau]

I checked and it's actually 16amp at the MCB, should this go lower?

 

[Mud Hut]

this work is notifiable under Part P of the building regulations

ColJack, at the risk of asking what may already have been asked elsewhere, when did this law come into effect? And i assume it's not retrospective.

 

[RF Lighting]

//www.diynot.com/wiki/electrics:part-p

 

[stem]

I checked and it's actually 16amp at the MCB, should this go lower?

You can have a 16A MCB in the consumer unit as long as you have a Fused Connection Unit with a suitable fuse and isolation in before the pump. Depending on the rating of the shower pump. (Most take in the region of 250W about 1 amp).

If yours has a similar rating, the answer to your question is yes. You need A 3A fuse before the cable feeding the pump.

The MCB protects the equipment and cable supplying it from overload. My guess is that you don't have 10mm cable connected to the pump terminals so it will probably have changed to flex somewhere, if so you may have flex rated at 5A. Imagine your pump develops a fault that draws 16A. At this a 16A MCB will not trip, 16A will be flowing into an appliance rated at 3A and a cable designed to carry 5A. This is how electrical fires start.

This is very basic electrical safety knowledge, if you don't have this I would suggest that you don't attempt electrical work for the safety of yourself and your family.

 

[billau]

Thanks for your help, I've tackled plenty of electrical work in the past and always consider safety first. This particular shower installation was done by a registered plumber and not me, but following your advice I will put in a 3a (or maybe 5a) fused spur which I can then use to solve the UFH connection problem as well. Thanks again.

 

[billau]

OK, one last question on this then. I checked at the shower switch and it's 10mm cable to the switch and from the switch to the shower. So, I plan to replace the 16amp breaker at the CU with a 5amp breaker, then run 2.5mm cable from the shower switch via 3amp switched FCU to the Under Floor heating. Is that OK, particularly wrt having 10mm cable and 5amp breaker?

 

[billau]

You've all gone quiet guys, reading back some posts the above seems OK to me, can someone please confirm before I head off to buy the bits?

 

[stem]

What you suggest doesn't sound dangerous to me, but it's a little unorthodox. There's always a danger that someone at sometime in the future might not understand what you've done.

Perhaps no one's replied because they don't really like it, but can't say that it's dangerous.