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.

 

[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).

 

[EastAnglian]

No need for the 60A fuse, take it out of the equation. 2 off 100A connector blocks (much nicer to work with than a Henley block), keep the double insulation inside the JBs, no need to box them. Job done.

 

[davesparks]

No need for the 60A fuse, take it out of the equation. 2 off 100A connector blocks (much nicer to work with than a Henley block), keep the double insulation inside the JBs, no need to box them. Job done.

So you have checked the cable calcs and the Zs etc then have you?

And what do you mean by 100A connector blocks? I've not seen them before but they sound dodgy! How exactly do you terminate SWA into them without the need for an enclosure?

 

[EastAnglian]

And what do you mean by 100A connector blocks? I've not seen them before but they sound dodgy! How exactly do you terminate SWA into them without the need for an enclosure?

Cable calcs have been dealt with by earlier posters, no need to repeat.

Thanks for reminding me the incoming cable is SWA, which of course needs correct termination.

A link to those dodgy connector blocks (but not my supplier!):

100A Single Pole Tails Connector Box - Single Pole

 

[davesparks]

Cable calcs have been dealt with by earlier posters, no need to repeat.

Thanks for reminding me the incoming cable is SWA, which of course needs correct termination.

A link to those dodgy connector blocks (but not my supplier!):

100A Single Pole Tails Connector Box - Single Pole

They are single pole Henley blocks, you said they were a better alternative to Henley blocks !

Cable calcs haven't been dealt with, there have been no details as to any apical rating factors yet.

 

[EastAnglian]

They are single pole Henley blocks, you said they were a better alternative to Henley blocks !
.

Since they are made by Click I don't really suppose they are Henley blocks at all!

Horses & courses, but I find it easier to fit 25mm tails into these than the double decker ones, especially if there are already existing tails terminated.

Cable Calcs - too much wine, I don't do calcs after drinking ;-)

 

[davesparks]

'Henley block' is a common term for what would be better described as a 'service connector block' also known as Lucy, ESCO or mains blocks.
All available in single or double pole versions

 

[EastAnglian]

Just as there are many vacuum cleaners but only one Hoover, there's only one true Henley :conehead:

Insulated Connectors Boxes | WT Henley

 

[davesparks]

But by the same token we all know what is meant when someone says Hoover, Henley block, megger, spanset, bulb etc
They have become common names for a type of product.

 

[andyelectric]

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

Does he need RCD protection?

Hi Marvo, submain from 80a SF to 60A SF is run in swa in cable tray in cellar. From 60A to consumer unit is tails in open air. So no rcd required except fro CU to showers.

 

[andyelectric]

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

This is exactly the sort of answer I am after. 2 electric showers in a house is a common enough occurence(there were 2 in my last house , and I expect many of these setups are running on 60A fuses in the cutouts)

My feeling is that it is very unlikely that the 60 will ever blow. It will be a rare occurence for the 2 showers to be running at the same time. However being a newbie 'tired' fuses are not something I have come across.

However, as it will be relatively easy to remove the 60A from the equation I think I will do this and fit the second shower.


However,