Can i run a spur from an immersions fcu

[mancduff]

I was going to run a spur from the immersion heater's fcu to a 3amp fused double pole for a mira wall mounted power shower, will this be safe to do.
I thought with it being only 3amps that it wouldn't be a problem but read somewhere else on the forum that it might not be advisable. Any thoughts on what i should do coz the misses is giving me right ear ache over it.

Thanks

 

[RMS]

What sort of load does the shower run at?

 

[mancduff]

Thanks for the reply this is from the manual.

Appliance power supply - 230-240 V, 50Hz, fused at 3 Amps, via a double pole
switched fused connection unit (not supplied) with a minimum 3mm contact separation
in each pole.

Power supply connection - The Event XS is fitted with a terminal block which will
accept cable up to 2.5mm2. Minimum cable size (cross-sectional area) required
under normal installation conditions is 1mm2.

Absorbed power - Approximately 150 W under normal working conditions

 

[securespark]

No.

The OSG says something like water heaters in excess of 15 litres must have their own circuit.

 

[RMS]

Securespark, the on site guide does state this but can you find it in the BS7671?

If this pump does run at approx 0.625A then i think it would be okay to wire off the immersion heater by means of supplying a switchfuse spur with a 3amp fuse fitted.

Its maybe not the the best practice but the overcurrent protection is still adequate for the cable (presumably 2.5mm cable protected by 16amp mcb) and the design current is does not exceed the overcurrent device rating.

RMS

 

[kai]

This is perfectly safe, provided that the shower draws 3 amps or less, and the immersion draws 13amps or less.

Both items are resistive loads, and Ib <= In <= Iz, so perfectly safe.
13amp + 3 amp = 16amps, i.e. the B16 MCB breaker is suitable.

 

[RF Lighting]

"..if you're gonna do it, do it right, right?"

 

[securespark]

If you're having a dig at my strictness, I was brought upon the 15th, and we were told never to put any other equipment on a radial circuit supplying fixed or stationary equipment. Ie, showers, immersions, cookers etc... The NIC still stick by this.

 

[RF Lighting]

Not a dig at all.
I agree with the sentiment fully.

 

[mancduff]

Thanks for the replies, i think i'm just gonna have to try off the immersion coz after lifting up floorboards the only cabling i came across was the biggun for the cooker and i no not to spur off that - no ring circuits nearby and i can't run it off a lighting circuit so the only supply i can run a spur off is the immersion heater which i'm sure is connected straight to the circuit board which have mcb's.
If you see anything wrong with this approach or have suggestions i would be grateful.

 

[mancduff]

After a bit of trial and error switching on and off fuses i discovered that the cable i thought was the cooker cable is infact just a radial circuit cable serving the washing machine and one socket, the cable i think is 4mm twin core so i used this instead of immersion socket for shower. I've joined them in a junction box
http://www.flickr.com/photos/mancduffstuff
What i want to know now is if i can spur off this with 2.5mm or does it have to be the same size cable in the junction box.[/url]

 

[RF Lighting]

What size is the fuse in the fuse box that isolates this supply?

 

[mancduff]

Its on a hager mcb trip switch not sure of the fuse, doesn't say on the trip switch the power shower only pulls about 3 amps.

 

[mancduff]

i know for certain that only the washing machine (which i'm sure just uses hot water no element) and one socket for the fan in the kitchen that was taken out so is not in use as its at the top of a kitchen unit out of sight are the only things running of switch, have no idea why the electrician who did the job used 4mm must be coz its radial - it actually looks like 6mm.

 

[securespark]

It would be advisable to use the same size cable. And check that jb is rated at or above the protective device value.

IE if your protective device id 30/32A, make sure your jb is 30/32A rating.

And fuse down the pump with a DP switched spur, fused at whatever the manufacturers recommend - 5A?