MCB for immersion heater?

[tarquinlinbin]

A friends house has electric heating with an immersion heater for hot water. The house was one of those built circa 1985 with only electric and water services. The heating and hot water are via economy seven and there is an old venner electro mechanical timeswtich fitted for the off peak rate switching. The timeswitch is two hours behind,presumably over the years it has drifted out. I would have thought that it would have been replaced by a radio teleswitch by now??,its wire sealed,i wonder if it would be a major issue if i broke the seal and reset it or could i request them to fit a radio teleswitch?

Other point, the consumer units (one for normal rate the other for the heating/immersion are all wired type fuses except that the immersion heater has a fuse holder containing a cylindrical cartridge type fuse,presumably its a quick blow fuse or something? could i just remove that and fit a 15 amp mcb in its place?,i intend to wire the immersion back into the day rate consumer unit. It was originally wired to day rate but the occupier decided to have it wired to the night rate meter which makes it very inconvenient if you run out of water during the day as there is no bypass switch!!

joe

[Dave Jones]

Why does it matter if its 2 hours out?

Yep

i intend to wire the

most E7 systems have two immersion heaters intalled, one at the very btm of the cylinder for E7, and one at the top for back up on day rate.

It was originally

[tarquinlinbin]

because it doesnt switch on now until about 0100 hours whereas its actually set to 2300 hours so i could potentially have a late bath/hot water but waiting until 0100 is a bit much..

not this one im afraid...

[Andy Wade]

You should request that they correct the E7 switching times, so that they're within the advertised window. IME they'll almost certainly replace all the metering equipment. You might or might not get a radio teleswitch, depending on what's in vogue with the local distribution or meter operator company.

That's a BS 1361 cartridge fuse (not particularly quick blow). Perhaps a former rewireable fuse carrier overheated and had to be replaced, or maybe it's down to what was in the van at the time of first installation.

You can get plug-in MCBs to fit Wylex CUs so yes you could. But why the need? Rewireable and cartridge fuses are still perfectly satisfactory if not abused. MCBs are trendy and convenient, but don't give any better protection in the context of an immersion heater circuit.

The usual arrangement is to use an Economy 7 controller. Essentially this is just a time switch which you ensure you keep sync'd to the actual E7 switching times, but it also provides for timed daytime boost. Alternatively, if your cylinder allows, use two (electrically separate) heaters, one at the bottom of the cylinder on the switched supply and a boost heater at the top on the permanent supply, via a time switch.

PS: don't refer to the non-switched CU as day rate - this leads to endless confusion as seen in a recent thread.

[Christian McArdle]

I'm not sure I agree. The rewireable fuses I've seen blow have been nothing short of a fire risk.

Christian.

[Andy Wade]

In what way?

[Christian McArdle]

In the bright white light, smoke and leaving scorch marks over the mounting board sort of way.

Christian.

[Andy Wade]

Impressive flashes and bangs sometimes, but for proper semi-enclosed fuses made to BS 3036 there's no significant fire risk surely. There's a century or more of experience of using rewireable fuses; ways not to make them were weeded out during the first half of the 20th C. The Wylex design has been in use since the 50s or 60s without much modification, AFAIK. Their use in new installations is still permitted by BS 7671.

MCBs also vent hot gas from an arc chamber when interrupting high fault current.