I may have used E7 as a generic term,
I think everyone would have expected the system to be wired 'normally'.
Strange Immersion Heater Wiring
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As the premises is heated by fixed fan heaters and a central air source heat pump. (no storage heaters) everything needs to operate during the day, so there isn't a separate off peak distribution board.
From everyone's comments it does seem that it is a bit of an odd installation, so we will rewire the top element to a permanent supply and use the time switch to control the bottom element. Job done.
Whilst we're at it, should we change the DP isolators for DP FCU's or is a 32A MBC OK for direct connection as presently? Bearing in mind that the immersion elements are wired in 2.5mm2 HR flex
From everyone's comments it does seem that it is a bit of an odd installation, so we will rewire the top element to a permanent supply and use the time switch to control the bottom element. Job done.
Whilst we're at it, should we change the DP isolators for DP FCU's or is a 32A MBC OK for direct connection as presently? Bearing in mind that the immersion elements are wired in 2.5mm2 HR flex
Arguably, yes, for the reason you give - 2.5mm² flex is not adequately protected against overload by a 32A MCB. However, it could also be argued that an immersion element is not able to create an overload (only a 'fault', against which you would probably have adequate protection).
Given that both immersions are being fed from the same 32A circuit, you are essentially stuck with the rather unusual 'doubled up' 2.5mm². If you had a spare 'way' available in your CU, you could separate them into (somewhat more conventional) two separate 2.5mm² circuits, each with a 16A or 20A MCB - one for each immersion.
Kind Regards, John
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Maybe you should use a boost timer for the top element so it can only be turned on for a max of 2 hrs and you wouldn't need to remember to turn it off.
They also do a 4 hrs one which maybe more suitable
I think the confusion is that everyone thinks its an offpeak system.
Clearly, its not.
Its just a water tank with two immersions that run during the day when hot water is required.
If the rest of the buildings using peak rate heating, why would they have bothered with E7 just for the water tank?
Clearly, its not.
Its just a water tank with two immersions that run during the day when hot water is required.
If the rest of the buildings using peak rate heating, why would they have bothered with E7 just for the water tank?
Conceivably, but the OP has referred to 'off peak electricity/rate' on several occasions, and various things he's written have also implied that he probably does have a dual rate tariff.
The usual reason for such a situation is that the house once had storage heaters, but no longer has, but no-one has bothered to change the tariff - an oversight which is probably costing them money.
Having said that, I am in such a situation. Very many moons ago (until I moved in), my house had storage heaters and an E7 tariff. I got rid of the heaters, but have (so far) retained the E7 tariff, because (in my case) it remains (albeit only just) cost-effective to stick with E7. However, that's only because of my pattern of electricity usage, which is probably pretty atypical. For most people, E7 (or similar) without off-peak heating will usually be costing them money.
Kind Regards, JOhn
Yeh, but its not a house, its an office block/commercial premises.
Maybe the OP himself has made the assumption that its off-peak, when the wiring and lack of any other off-peak heating suggests that infact its not.
Maybe the OP himself has made the assumption that its off-peak, when the wiring and lack of any other off-peak heating suggests that infact its not.
Thanks Guys
We do have off a dual tariff meter, but not a separate distribution board that is only powered during the off peak time.
I mentioned before that there are not, and never have been any storage heaters. The premises are only 8 years old and in 'as built' condition.
Space heating is air source heat pump, which does use the off peak when we have to leave it on over night in sub zero weather.
If the time switch is set only to be 'on' during the off peak tariff, then it is an off peak system isn't it?
I just thought it was a bit odd compared to the usual twin immersion set up I have seen. It's not as if the cylinder is supplying a bath house or anything, just a few sinks, so one 3kW element is more than sufficient, we don't need 6kW.
We do have off a dual tariff meter, but not a separate distribution board that is only powered during the off peak time.
I mentioned before that there are not, and never have been any storage heaters. The premises are only 8 years old and in 'as built' condition.
Space heating is air source heat pump, which does use the off peak when we have to leave it on over night in sub zero weather.
If the time switch is set only to be 'on' during the off peak tariff, then it is an off peak system isn't it?
I just thought it was a bit odd compared to the usual twin immersion set up I have seen. It's not as if the cylinder is supplying a bath house or anything, just a few sinks, so one 3kW element is more than sufficient, we don't need 6kW.
.
That's certainly what I would call it.
... and I think that most of us who have commented have agreed that it's very odd - and difficult to understand what it was meant to achieve. Mind you, it's also odd to have the "doubled up 2.5mm²" 32A circuit supplying the immersions, rather than a 4mm² circuit or two separate 2.5mm² circuits!
Kind Regards, John
True, I had forgotten that.
As you will have seen, the OP has now clarified this point.
Kind Regards, John
Come to think of it, my immersion heater was wired from B32 MCB to timer with 2.5mm t&e, then from timer to isolator with 1mm t&e + 3c&e, and then flex to the immersion heater.
Well, assuming that you mean 'single 2.5mm² (and not 'doubled up' as in OP's case), that's obviously essentially 'all wrong', probably non-compliant and, many would say, potentially dangerous. A B32 is too big to provide overload protection for 2.5mm² cable (and, unless it is massive, the flex), let alone 1mm² cable (unless, of course, one argues that an immersion heater cannot create an overload!). The 1mm² itself may be just about adequate for an immersion, depending upon installation method.
Kind Regards, John
K
kai
It makes sense to swap out the breaker for a B16 at the source end, a B16 breaker is more than enough to power a 3kw immersion with spare capacity remaining.
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