I will be having a Bosch Greenstar Boiler fitted and currently only have a 5core cable to the boiler position. My question is can i join N, Ns and Nz (pump neutral) together at the boiler to reduce the numbers of cores required ?
Bosch Greenstar wiring
- Thread starter RichardShelley
- Start date
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Deleted member 267285
Some more information would help, such as which system you have or will be having. There’s usually no reason why not, but you might be joining terminals unnecessarily. Is your installer not doing the wiring?
Are you familiar with Bosch Boilers. It's a heat only boiler feeding a vented system on Y-Plan and 3-port valve doing C/H and HW. Controlled by a programmer on an industry standard backplate. 240 volt supply is from an FCU to programmer and from there to boiler and also to programmer. Cable to boiler is 5-core (inc earth) and cable between programmer and wiring centre in airing cupboard is 7- core (inc earth). Wiring the Bosch Greenstar boiler according to their wiring diagram needs more cores on both of the interconnecting cable. If I could common up the three neutrals (N, Ns and Pn) in the boiler I would have enough cores. No other boilers seem to do it this way ie with three separate neutral terminals). I am a Part P qualified electrician (using NAPIT).
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Deleted member 267285
Yes I am with some, but as per Andrew, everything else is wiring center.
Part P is a building regulation not a qualification.
Please look at my original question. I know that other boilers can be done with a five core. My question is can I join N, Ns and Np together in the boiler and just use one neutral away from the boiler. There must be a reason why Bosch Greenstar separate them ? I'd like to know what the reason is and can I override it by joining the three separate neutrals together. Along the way I've have seen something that suggests that Bosch want the feed to the wiring centre and pump to be "isolated" from backfeeds. I'd like expert confirmation that this can be circumvented by "commoning" the three separate neutral terminals. I don't want guesses or ill thought suggestions.
I know how a conventional boiler is wired with 5 cores. However if I only use 5 cores them I'm not keeping N, Ns and Np separate in the way that Bosch. I am trying to understand why Bosch separate them onto separate terminals. Once again I'll state my original question. Can I loop N, Ns and Np together at the boiler terminals and if so what are the implications ? At the moment responders are not showing that they understand electrical stuff. The way Bosch set out the connections on some (not all) of their boilers this is difficult to understand and I am trying to understand why. By the way CBW I only used Part P as my qualification because it is in common use. I have B Tech and HNC in electrical engineering. Please answer my question rather than challenging my qualifications. What are your electrical qualifications and do you know enough about central heating wiring to actually answer my question ?
bosch separate them to allow control of external controls, NS is neutral send to external controls, LS is live send to external controls, means the power can be cut when the boiler is switched off, you can also connect pump neutral to the boiler or in the wiring centre, as already said you can common all the neutrals,
Thank you Picasso. So if I common the neutrals in the boiler the power to the lives will still be cut when the boiler is switched off at the boiler controls in the way that Bosch require. ie communing the neutrals will not affect what Bosch are trying to achieve ? Thinking about it in that case the power to the lives will still be cut off just not in a double pole way (ie neutrals as well). Is that correct and OK ?
There were no guesses or ill-thought suggestions from me, and I understand electrical "stuff" perfectly well thank you. I have my Part P, 18th Edition A2 regulations, Initial Verification, and Inspection & Testing qualifications. I also have 17 years experience of wiring boiler control systems of far greater complexity than this. The way I've suggested is perfectly acceptable and works well. By all means do it your way if you like, but it's totally unnecessary.
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I still don't see how you think joining the 3 neutral terminals together in the boiler is going to make even the tiniest bit of difference to anything? You've only got 5 cores so you're going to have to join them all together in the wiring centre anyway
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Deleted member 267285
I’m not questioning your qualifications, a lot of people seem to think part p is a qualification rather than a building regulation. You and Andrew will clearly know more than me, but he has already answered your question.
Muggles that's not correct. If you wire it the way Bosch want then N would be the Boiler neutral, Np would be the pump neutral and Ns the neutral for everything else in the wiring centre ie Programmer etc. That's the whole point Bosch want them kept distinct.
Have you asked Bosch? That might be a good place to start.
Apparently they're very tight lipped about technical design details like this. They'll help with faults and operating stuff but not design details.
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