Diversity and Showers

[andyelectric]

Hi, please be kind to this Electrical Trainee fresh out of the forces. This is my first question on the forum. One thing that was not discussed in depth on my course was diversity, and reading up there seems a fair bit of subjectivity and difference of opinions on it.

Now that I have my shiny new quals the missus has requested I fit a 2nd electric shower. We currently have a 10kw fitted, and she'd like the same again. Flat has gas heating and cooker, so other loads would be normal household appliances. Both showers would be used as we have a lodger, but would in all reality rarely be used at the same time. Worst case would be both on at the same time for 10m whilst the kettle and washing machine etc were on.

My current supply is as follows. 100A from cut-out(I saw the fuse go in). 80A switch fuse supplying submain run in 16mm swa. Another metal 60A switchfuse then into CU. (Reason for 2nd SF is that it was there already and used as a handy termination for the swa when meters were moved).

My feeling is that I'll be ok with the 60A. I could quite easily change the 2nd SF for a metal adaptable box and henley though, thereby uprating my supply to 80A.

Would you guys on here recommend removing the 60A SF.

 

[Farmelectrics]

install your shower highly unlikely to be using everthing at once have a good read of the on site guide theres a chapter or a page about diversity in there diversity is sometimes left to the installer to work out using your past experiences

 

[Octopus]

I think you should consider a "pumped" shower and use the hot water from your tank!

 

[Marvo]

I've removed several off-topic posts. Please either stay on topic or stay off the thread entirely. Thank you.

 

[shanky887614]

I think you should consider a "pumped" shower and use the hot water from your tank!

a pumped shower has higher water pressure and is nicer to use.

if you want a 10kw electric shower then at 40amps it should be ok depending on installation method etc.

i would suggest swapping the 60amp isolator for something bigger, it shouldnt be a problem because i doubt it will get warm unless it is used for a long time.

 

[andyelectric]

Thank you Marvo for cleaning up the thread.

Murdoch, unfortunately my combi-boiler although perfectly suited to my hot water and heating needs cannot support a shower and I do not have a hot water tank from which to run a thermostatic shower.

From research it would seem that diversity is a pretty subjective subject. The OSG seems to me pretty prescriptive, but on google I have found some pretty common srnse arguments backed up with reasoning that 60 amps may be ok for 2 high power electric showers.

However I obviously have no experiemce in this area. So I have 3 choices.

1. Fit the 2nd shower on 60 amp supply.
2. Fit with 2nd S/F removed on 80 amp supply (my present favourite).
3. Do not fit 2nd shower.

Each of these 3 options is dependent on diversity, and I was hoping to pick up on reasoned (reasoned being the operative) arguments on the best way to proceed.

Cheers Andy.

Apologies for typos, on phone.

 

[ruston]

Forget the electric shower, treat your family and run it as others have said from the gas, no one will use the other electric one after they have used the higher power gas powered one.

Sorry I must have cross posted with you.

 

[andyelectric]

Just thought I'd add. I'm fine with choosing cable, mcb etc, and fitting shower, just I have no experience on the weakening of fuses which is what I am most worried about. (ie I don't want to blow my 60amp fuse 2 years down the line and be in stook if I could have simply upgraded to 80 amp.)

 

[davesparks]

Is the submain relying on the 60A fuse or is it suitably sized (bearing in mind route, VD and max Zs) for 80A?

 

[andyelectric]

Meaured Ze at the board is 0.31 ohms, and the run to each 2 showers are under the ground floor joists(so pretty cool for cable). No problem with cable runs as both pretty short runs compared to an up round the loft and down type.

The submain relies on an 80 amp switchfuse, DNO fuse at cutout is 100A, the only reason the 60 amp is there is that it was remaining in the cellar from a meter move. The 60A SF could be reasonably easy enough be removed thereby upgrading supply to 80A.

 

[davesparks]

Ok so your Ze is ok, but what is the Zs of the submain/Zdb of the board?

The submain is currently operating on the 60A fuse for overcurrent protection whilst the 80A will be providing fault protection.
The way you describe the situation this was not intentional, but that is the way it will operate anyway.

Are you sure the 60A fuse wasn't replaced with a solid link at the time the work was done ?

 

[benji]

isn,t there types of switches that prevent two showers being run at the same time ??

 

[davesparks]

isn,t there types of switches that prevent two showers being run at the same time ??

There are, but there is no need for such fancy nonsense in this case.

2x electric showers + normal domestic loading won't bother an 80A fuse for a good few hours.
Probably won't bother a 60A fuse for quite a while either but then it will probably become 'tired' after a while

 

[Lucien Nunes]

Concur, it will work but the 60A fuse will be stressed from time to time, while the 80A probably won't. Rip out the SF and carry on.

 

[Marvo]

Does he need RCD protection?

 

[davesparks]

Does he need RCD protection?

Yes, but as a fully qualified 5 week danger he presumably knows this already.

 

[Marvo]

As a qualified African I thought he might but wasn't 100% certain

 

[andyelectric]

Ok so your Ze is ok, but what is the Zs of the submain/Zdb of the board?

The submain is currently operating on the 60A fuse for overcurrent protection whilst the 80A will be providing fault protection.
The way you describe the situation this was not intentional, but that is the way it will operate anyway.

Are you sure the 60A fuse wasn't replaced with a solid link at the time the work was done ?

Dave, the 60A is as a have said. It is an mem jobbie from 40 years ago. Pulled the fuse last week and changed the cu. ji

 

[davesparks]

Dave, the 60A is as a have said. It is an mem jobbie from 40 years ago. Pulled the fuse last week and changed the cu. ji

Ok so it's not been replaced with a link then, why didn't you gland the SWA directly onto the CU when you replaced it? Far better than having the unnecessary switchfuse left in place!

And how about that Zs on the submain?

 

[telectrix]

fit shower, dump the 60A fuse. 80A fuse will stand a 50% overload for longer than a shower runs ( assuming no teenage daughters. that could be fun when shower goes freezing cold when they stay in it for yonks).