two supplies to one element.....RCD question

[Nicky Tesla]

Hello i am to replace a DB soon where there is currently a separate fused isolator and an old dual tariff boost switch, for the water heating element. The E7 time comes from the separate E7 radio telemetry switch meter and therefore has different supply tails than that of the main board.

The element receives its power from the boost switch from either of two sources, the main DB or the SFI then on to the element via a single T&E.

The problem is, how can i wire the new DB so that the RCD main switch doesnot go off, when the other supply comes in, which was not a problem before the need for RCDs. I assume that the old E7 switch may have a common neutral terminal which may cause this.

My thoughts are a smaller seperate DB, within it 2 main switches feeding 2 seperate 15A mcbs, which then go straight up to the old switch. Then the cable to the element coming back down to a 61008 RCD and back out again for the final to the element.

This seems a bit OTT so can anybody think of a better way ? ?:|

 

[sparkytim]

Ditch the Off peak supply and fit a Horstman Q7 timer unit off the 24 Hour supply.

 

[steptoe]

tim, that wont allow for the leccy board switching your off-peak at different times though.

 

[Nicky Tesla]

I may even try to get the tenant to get a more modern meter which just needs a single supply but only one meter.....will that cost him?

 

[ProDave]

See the discussion in another thread.

The Horstman boost controller normally connects the heater to the off peak supply so it's ready to be powered up overnight (or in a daytime boost for E10)

When you rotate the timer dial, a double pole switch changes over to feed the heater from the permanent supply until the timer's time expires.

So if it's wired properly you should not have any issues with dual supplies and dual RCD's.

 

[Nicky Tesla]

So if it's wired properly you should not have any issues with dual supplies and dual RCD's.

I hope so Dave, it will make things easier.

But still, does changing the meter to a single meter cost the occupier, cos its a big ugly thing ( i mean the meter)

 

[ProDave]

But still, does changing the meter to a single meter cost the occupier, cos its a big ugly thing ( i mean the meter)

If you change to a single rate meter, then you will get charged the peak rate all the time. So you might as well ditch the storage heaters as there's no value in them. The heating costs will go up, and the tenant will complain.

NEW installs seem to be done now with a dual rate meter with a built in radio time switch, so it's nice and neat. I guess you could try and ask for an upgrade, but chances are, if your setup (old timeclock and separate meter) still work, they will say no. Unless you offer to pay them.

The usual solution to untidy metering is a cupboard.

Sometimes if you have a valid reason for needing a meter moved, you might get an upgrade to modern kit, but even that is not guaranteed.

 

[Nicky Tesla]

Yes thats what i mean, a dual rate meter.

It is in a cupboard with all the coats and hoover etc but it just looks a mess and i like to do a nice job. There would deffo be no rcd prob then as the neutrals will be from one source. The electric costs should be cheaper also as the whole house would be benefiting from off peak rate after 12 and not just the ST HTRs.

 

[ProDave]

With Economy 7 or even Economy 10, the WHOLE house gets the cheap rate over night. So if you can stand the noise, put the washing machine and tumble dryer on over night, and get up early for your morning shower.

If you are implying that your present setup does NOT have the house all on the cheap rate, then it sounds like you have the old white meter system. With that, there was one meter (normal rate) for the main fuse box, and a second, completely separate meter (fed from a tine switch) for the off peak fuse box.

If that's what you have, get a free upgrade to Economy 7, and you will get nice new meters and a much tidier setup.