replacing 8kw shower

[elliebelly]

Can someone advise us please? We have to replace our worn out existing shower which is 8kw. Can we put in a 8.5 kw with the existing rating which is 32amp fuse?

 

[sparky (sfd)]

40A breaker for a 8.5kw




7.5kW – (32A MCB rating) 7.0kW – (32A MCB rating)
8.5kW – (40A MCB rating) 7.9kW – (40A MCB rating)
9.5kW – (40A MCB rating) 8.8kW – (40A MCB rating)

 

[yankey-sparky]

Is he going to have to upgrade his wiring to handle the larger fuse/MCB?

 

[breezer]

depends how big the cable is now, if its 6mm its on the borderline 10mm will be better

 

[securespark]

6mm2 T & E is rated at 46A in the regs, clipped direct. Assuming there are no correction factors like ambient temperature a rewireable fuse (BS3036) or cable runs in loft insulation, 6mm2 is adequate up to 10.8 kW (45A).

Got to watch for voltage drop, but that aint a problem in 99% of cases, cos you have a max of 4% voltage drop on 240 V (ie 9.6V) and you'd have to have a circuit length of well in excess of 25m to achieve that figure loss.

 

[elliebelly]

Thankyou for the replies to my previous query regarding replacing our shower,your help is much appreciated! As I am disabled and cannot use the bath this shower problem is turning into a nightmare. I can offer the following if this will help. I am a useless female where electrics are concerned so please bear with me.
When the house was rewired the charts show the following.(please note the shower was not rewired as we had it redone only a short time previously)
Shower-wiring-pvc.points served-1 max permitted disconnect time 4
bs(en)type no 60898/2 Rating 32 live 6.0 cpc 2.5 (mm2) phases neutral 200 phases earth200 neutral earth200 max measured earth loop .26
The cable for the shower runs up the wall from the fusebox into the loft and across to the bathroom. There is a separate pullcord for the shower. I suppose the length of cable would be something like 10 metres max.
Thankyou for your patience and help.

 

[il78]

Calculated using Amtech Single Cable

For a 8.5kW Shower / Reference Method 1 (clipped / bunched / enclosed)

Cable Size 6.0mm
Voltage Drop 2.43 (max length 37.0m @ 4%)
Max Cable Rating 47Amps (if in conduit 41Amps)
Device Rating 40Amps


Regards,

Ian

 

[sterose]

6mm2 T & E is rated at 46A in the regs, clipped direct. Assuming there are no correction factors like ambient temperature a rewireable fuse (BS3036) or cable runs in loft insulation, 6mm2 is adequate up to 10.8 kW (45A).

Got to watch for voltage drop, but that aint a problem in 99% of cases, cos you have a max of 4% voltage drop on 240 V (ie 9.6V) and you'd have to have a circuit length of well in excess of 25m to achieve that figure loss.

6sqmm cable will do fine for 8.5kw showers, but no more than that. Change the MCB to 40amp too.

But, remember what I always say: "why take a chance". If a certain method of wiring is dodgy, be on the safe side, and do it properly. If your worried about, for example, cost of new bigger cable, you can get a run of about 20m 10sqmm for £20 from a wholesaler.

___________


Next, to my 'experienced' forum comrades. People who we give advice to are not electricians, and sometimes not even competent DIY'ers. They do not need to know about voltage drop in cables or any other technical fact, unless they ask specifically about the theory or have a problem that actually relates to technical facts.

When people who do not understand basics are given 'technical' facts, the shutters come down, and all they hear is that, in this case, you can use 6sqmm for up to 10.8kw. Dangerous.

The fact of the matter is that rarely is the cable allowed full rating because of de-rating factors. So why put the idea into peoples heads that they should push cable or equipment to the limit when it is likely to push their luck to the limit?

Everyone should consider 10sqmm cable to be the ABSOLUTE MINIMUM for showers over 8.5kw. AND NO-ONE SHOULD EVEN ENTERTAIN THE IDEA OF USING 6sqmm CABLE FOR 10.5kw SHOWERS.

 

[securespark]

sterose

"If a certain method of wiring is dodgy.....do it properly."

Resent this comment. My methods are not dodgy. I have been doing this job professionally for 16 years and never had any problems or comeback etc with any of my work.

Sure, you can go ott on cable sizes, but if you don't have to, why do it?

In some installations, replacing the cable would present many practical problems. It's not just about the cost of a few metres of 10mm2 T & E.

The figures in the regs are worked out to be safe, even if the cable is working at its limit. As long as the other requirements are dealt with correctly ie upgraded MCB , an RCD, making sure the CU isolator is 100A and possibly the main fuse as well, as well as the obvious main and supplementary earth bonding, then the job is a good one.

 

[phil28]

don't forget the 10mm earth cable to earth bond the bath/bathroom pipes if you are going to stand in one for your shower and an inline rcd is always a good idea to add.
more cost but that is what any spark worth his salt would install.

 

[securespark]

can use 4mm2 for supplementary bonding (connecting metalwork within the bathroom to each other) and 10mm2 for main bonding (from main earth terminal to gas pipe, water pipe, and any other service pipes. Other things to be bonded to the main earth terminal include any metallic vent ducting or accessible structural steelwork, ie exposed rsj (rolled steel joist), etc...

Don't forget to link all metalwork together in the bathroom including (if applicable) bath, metal wastes, h & c pipes, airing cupboard, immersion heater earth terminal, shower earth terminal, central hearting pipes, radiators etc. You should even consider linking to earth wires feeding shaver sockets, light fittings etc.

Please note that this list is not exhaustive!

 

[sterose]

sterose

"If a certain method of wiring is dodgy.....do it properly."

Resent this comment. My methods are not dodgy. I have been doing this job professionally for 16 years and never had any problems or comeback etc with any of my work.

Sure, you can go ott on cable sizes, but if you don't have to, why do it?

In some installations, replacing the cable would present many practical problems. It's not just about the cost of a few metres of 10mm2 T & E.

The figures in the regs are worked out to be safe, even if the cable is working at its limit. As long as the other requirements are dealt with correctly ie upgraded MCB , an RCD, making sure the CU isolator is 100A and possibly the main fuse as well, as well as the obvious main and supplementary earth bonding, then the job is a good one.

Sorry, securespark. Absolutely no implication of dodgy methods was intended. I was saying to all others who try dubious wiring methods for ease, to do it properly.

Perhaps my point was unclear.
What I was trying to say, is that you shouldn't induce people to push things to their limit, when may of them have no experience or understanding, and have no idea of what the item's real limit actually is - except what they have been told.

I always do things on the safe side (i.e. if 10sqmm is better, I use it), and perhaps a good slogan would be "the lesser experience you have, the bigger the cable you should use". Don't take it too literally, but you get my point.

I have seen dangerous things so many times, because people have bodged the job, because they dont understand the implicaions of their method. The ability to reason your actions, and understand the implications, only comes with experience.

 

[il78]

You should even consider linking to earth wires feeding shaver sockets, light fittings etc.

Dont consider......needs to be done....

 

[elliebelly]

Many many thanks to all who took the time and trouble to reply to my query,your help was invaluable. the result is one 7.5kw Mira Sports shower up and running. A big thankyou to Jewsons in Gt Yarmouth especially the lad in the bathroom section who knew his stuff and we ended up with what we wanted. Not so good Focus, Homebase, and worst of all Coopers (sorry to be customers we did not disturb your ignorance of us too much we hope) and The Plumb Centre who cannot get together and decide how long deliveries will take.