What shower power?

[DetlefSchmitz]

John, 'non-ohmic' is an accepted description of something where the resistance is not constant. Typically something like, say, a diode.

 

[PrenticeBoyofDerry]

Oh alright then, I'll also order a B40 breaker.

If the circuit is not covered by RCD protection, it maybe wise to consider purchasing an RCBO if your consumer unit is capable of having one installed.
It is very likely that the manufacturers instruction that come with your new shower will request the circuit is RCD protected.

 

[JohnW2]

John, 'non-ohmic' is an accepted description of something where the resistance is not constant. Typically something like, say, a diode.

Fair enough. However, despite what has recently been suggested, Ohm's Law always applies, even when resistance is not constant (i.e. when the relationship between voltage and current is not linear) - unless one goes to extremes and (as has been mentioned!) starts considering superconductors etc!

Kind Regards, John

 

[regsmyth]

Thanks for all your replies. I appreciate the maths too! Yes I am happy to change the breaker and it's back piece. I don't think I'll get an RCBO to fit the old Wylex CU, I like to live dangerously.

Thanks again.

 

[flameport]

Yes I am happy to change the breaker and it's back piece

If it's an old Wylex unit with plug-in MCBs, then it's unlikely a 40A MCB will be suitable, as a substantial number of those fuseboxes were only rated for a maximum of 30A per way.

The 40A device will probably fit in there, but using it with a high powered load such as a shower will result in the contacts overheating.

 

[JohnW2]

Yes I am happy to change the breaker and it's back piece. I don't think I'll get an RCBO to fit the old Wylex CU, I like to live dangerously.

You have introduced a new factor, which had not previously occurred to any of us, by mentioning that we are talking about an old Wylex CU with plug-in MCBs. As flameport has said, many of those were not designed (or rated) for more than 30A per way, so it's not necessarily safe to be running a shower >7.5 kW from it at all. Those CUs do sometimes catch on fire if excessively loaded.

The official advice would have to be to change things so that the shower was getting its power from somewhere other than that CU, and also to get RCD protection, at least for the shower (that could be achieved by, for example, having an additional RCD-protected mini-CU installed). If, despite that advice, you decide to stick with things as they are, given that the same current will flow regardless of the size of the MCB, the 'lesser of the evils' would probably still be to upgrade it from B32 to B40, which might result in it running a little cooler - but that approach would still have to come with a 'not recommended' caveat, given the nature of your CU. Oh - and, BTW, you wouldn't be able to get an RCBO for that CU even if you wanted to.

Kind Regards, John

 

[regsmyth]

Well I have ordered the 9.5kW shower now already. As far as I am concerned, I am simply replacing like for like, which appeared to have been ok for some time. I will take on board what you say, and check for any overheating at the breaker. The shower won't be heavily or frequently used.
If it seems to be a problem, I will consider the upgrade/reconfig options. I wrongly thought when I mentioned the breaker size/type, you would have realised it was one of these:

 

[PrenticeBoyofDerry]

The safest method would be to install a remote shower CU with the required protective devices, the manufacturer instruction will very much more than likely state that RCD protection be fitted to the shower circuit and yhis is something that should be followed.
With regards to the overcurrent protection, again your existing set-up is not suitable for a 9.5kW shower on a 40A MCB. Please do not ignore the advice been given and become one of those plug-in and play ignoramuses.

 

[THRIPSTER]

Looking at the rest of the OP's photo's would seem to indicate that there is a close interest in electrical work - for example the shots of melted 1.5mm² cable clips, design for kitchen wiring and other associated (dissembled) appliances - do all these pictures relate to the same property?


Regards

 

[regsmyth]

Thripster, this is a new house. I rewired the old place completely, following much advice from here, and with consultation from a proper spark. It was fully tested and signed off with no problems.

If the breaker starts to overheat, I will consider the alternatives, but I am simply replacing a 9.5kW shower with another one. Why should it suddenly become a major issue?

I'm not disputing the validity of the advice, but you guys are great at rooting us DIYers to the spot in terror. Keep it up!

 

[PrenticeBoyofDerry]

I'm not disputing the validity of the advice, but you guys are great at rooting us DIYers to the spot in terror. Keep it up!

It is more terrifying using your preferred methods, not the ones suggested by the knowledge on here.

If you are replacing a shower with one that is higher rated, that is not like for like, if you are considering replacing a 32A protective device with a 40A one, again not like for like and other things then need to be considered, such as loading of the cable, demand upon the board and Zs figures. Please do not ignore the info offered, again I will repeat myself, manufacturers instruction must be followed, and I will state again they are going to mention RCD protection.

It is preventative measures that have been recommended to you, not the reactive ones that you seem happy to abide to.

 

[regsmyth]

I am replacing a 9.5kW shower without RCD protection with a 9.5kW shower without RCD protection. That is like for like. Upping the breaker to 40A seems like a good idea to reduce the likelihood of overheating, which presumably didn't happen with the previous owner and a 32A breaker.

I will be checking the supply cable and the breaker for overheating, and if it seems there's problems, I will rectify.

 

[dhutch]

If you are replacing a shower with one that is higher rated, that is not like for like.

The OP states the current shower is rated "Supply 240V 9.5kW, Loading 230V 8.7kW" assuming the new 9.5kW shower is rated at 9.5kW at 240v then they are the same power.

I does seem that the board may be rated at 30amps max, and that for the mast x years/months the B32 MCB has also been overloaded. I cant comment on the implications for the board, nor would I ever recommend overloading a component as a plan-a, however the shower does appear to be being changed like for like.

The other thing seems to be; are we happy the cable has not been derated below 40amps to to routing and installation?

Daniel

 

[regsmyth]

Yes we are. The cable goes into the ceiling space, then up inside an internal wall and into the loft. Of course it might be wrapped in insulation and laid against a hot pipe, but again, I can only assume it's ok as the house hasn't exploded or burnt down yet. Thanks.

 

[THRIPSTER]

Hi Reg,

Do not think anybody is trying to frighten you - just advising.

From your answer I take it that the pictures of the Wylex consumer unit do not relate to the other pictures. I hope you did not mind that I looked at the other pictures but was trying to get a 'feel' for what is going on.

For what it is worth, and ignoring for the moment specifics relating to replacement of the shower, you have a 60A CU which probably would have been more than adequate when installed. However, with modern usage, cookers and the shower you may well find that the CU is sometimes overloaded. So, for what it is worth, I would recommend that you arrange for the consumer unit to be changed for one with RCD protection and so as to prevent any issues relating to over heating. Or, at least get the installation properly assessed.

Regards