Certification dilemma

[Taylortwocities]

If you mean an immersion, where does it say that?

It is not a reg. It is in the OSG (guide) 8.5

Says water heaters in vessels > 15litres blah blah "should" be supplied by their own separate circuit.

Methinks this is to guide against immersions being plugged into ring final circuits that have other loads, rather than to suggest that immersion heater radials must be dedicated to that function only.
FFS its a radial circuit. All circuit design rules re loads and diversity apply.

Got a 13amp immersion and a 3 amp pump on a 2.5mm radial circuit protected by a 20amp CPD?
Super, jobs a good'un.

 

[PrenticeBoyofDerry]

It is not a reg. It is in the OSG (guide) 8.5
Says water heaters in vessels > 15litres blah blah "should" be supplied by their own separate circuit.

Indeed, it is a guide (Appendix H). But there must be some substance/reasoning behind this guideline. As BS761 does not really cover this subject in detail, maybe could be from heat and controls within the plumbing sector? Thoughts to myself...... "Just because BS7671 does not cover it, does not automatically mean it is not covered by other regulations/standards".......!

 

[bernardgreen]

Maybe the logic is that an immersion heater supply may need to be fully isolated ( Live and Neutral ) when the heater develops a fault and this isolation would then prevent use of other items on the circuit.

 

[JohnW2]

Methinks this is to guide against immersions being plugged into ring final circuits that have other loads, rather than to suggest that immersion heater radials must be dedicated to that function only.

Indeed, and that makes good sense (having large 'fixed loads' on any sockets circuit is not really very sensible) - and this is covered in the regs (albeit only in the 'informative' App 15), which explicitly says that not connecting immersions etc. to ring final circuits is one of the steps which usually prevents circuit overload for long periods of time.

FFS its a radial circuit. All circuit design rules re loads and diversity apply. Got a 13amp immersion and a 3 amp pump on a 2.5mm radial circuit protected by a 20amp CPD? Super, jobs a good'un.

Exactly - and, like you, I don't personally believe that anything in either the regs or the OSG say that one can't do that.

Kind Regards, John

 

[pdhan]

Dop check the installation instructions for the pump and see if an RCD must be fitted. Most pump manufacturers mandate this.

Many immersion heater circuits are not RCD protected.

The pump manufacturer recommends it but they don't mandate it. Should one be installed though to comply with BS 7671?

 

[bernardgreen]

The pump manufacturer recommends it but they don't mandate it. Should one be installed though to comply with BS 7671?

It reduces the risks when thing go wrong. The pumps are designed to keep electrons and water apart but no telling what might happen out of sight.

A small leak could spray water into the motor. RCD trips and ( eventually ) you discover the leak which may otherwise have gone un-noticed until visible damage to walls or ceiling occured.

 

[Taylortwocities]

Circuits in a bathroom are now supposed to be RCD-protected.
One could argue that the connections are outside the bathroom but only the pump itself is there, and that is safely away, under the bath - so its never likely to get wet, is it

However, I make it a personal rule to always install an RCD where electricity, water and people mix, or could mix, if there's a fault. So I would want to see an RCD on that pump.

 

[EFLImpudence]

I can't believe there is any discussion or doubt on this subject.

Circuits can be designed for whatever appliances you require.

In this case the immersion and pump will both have double pole isolation and the pump can have an RCD FCU if necessary.

The manufacturer cannot, surely, stipulate that a new circuit be run for a 3A pump.
The manufacturer of the immersion will not have.



As for the OSG - well - it is full of statements which are to cover situations without having to think or design, i.e. for worst case scenarios.

If you don't know what size tails to fit, use 25mm².
If you can't do the adiabatic equation or read the regulations for earthing and bonding conductors, use 16 and 10mm² respectively.
If you can't work out the cable temperatures for maximum Zs let alone work out the Zs for mcbs from scratch, use these which are 80% values so will be safe for your 3A pump circuit.



As I've said before, I wouldn't have passed my annual assessment last year had I not ordered the new OSG on-line there and then. WHY?

 

[JohnW2]

I can't believe there is any discussion or doubt on this subject. ... Circuits can be designed for whatever appliances you require.

Exactly.

As for the OSG - well - it is full of statements which are to cover situations without having to think or design, i.e. for worst case scenarios. ... As I've said before, I wouldn't have passed my annual assessment last year had I not ordered the new OSG on-line there and then. WHY?

I presume because some Jobsworth has a very ill-conceived box to tick! As you imply, if they were really interested in having electricians who understand the principles, are capable of thought and capable of designing circuits which are compliant with BS7671, they probably should be asking their members to swear never to look at, let alone own, a copy of the OSG of any colour!

Kind Regards, John