Questions P.I (3036) and unusal voltage


Postby Sparkydelux » Fri Jul 09, 2010 3:56 pm

Hi all,

I am hoping someone can answer these 2 questions for me.

Firstly a Periodic inspection question. If a house has BS3036 fuses and I have identified this is and made them aware that they are on their way to becoming obsolete, at what point do they need to rewire / board replacement to comply with the current regs? I realise that its good practice to do the replacement but we cannot successfully 'sign it off' if theoretically it doesn't comply. What is the recommended route for dealing with houses that (may possibly be rented out) that have BS3036 fuses? I have also heard that if the system is healthy the owners do not have to modify to bring it to spec. Is this true? Its a bit of a contridiction to the 17th Edition then!

2nd question: I was fault finding on a circuit that had 240V across L&N BUT then when I went on to L&E the voltage went to 118V. What would have caused this? No EARTH or not connected back to the MET?

Advice and knowledge passed on is always appreciated.

Regards.

Sparkydelux
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Postby ericmark » Sun Jul 11, 2010 6:18 am

There is nothing wrong with BS3036 fuses. In fact I am about to change the B16 MCB to a Cooper Bussmann 10LCT fuse as the MCB is about as much use as a chocolate fire guard when the supply is from an inverter as it's I²t is too high. The 10A fuse has an I²t of 22A and a 10A B type MCB has an I²t of 50A.

Hence the fuse is not likely to disappear in a hurry. Din rail fuse carriers can be used instead of a MCB in many consumer units and for items like induction hobs it would make sense to use fuses.

The split board is very handy here as the fuses can be supplied from RCD and RCBO's can be used for other circuits.

The regulations are not retrospective and as long as the item complied with regulations at the time of design that is good enough. However old design can impact on the future designs so during a PIR we are required to highlight the changes and we have a code 4 specially for this. But there is a problem BS7671 only started with 16th Edition and you will note we call it BS7671 not 16th or 17th edition in all paperwork. So anything allowed before the 16th Edition can not be given a code 4 in my option. So for example a house build before 1966 with no earths to lights would still get a code 2 if all class II lights are used and code I if any class I lights are used.

You must remember you don't sign off with a PIR. Yes with installation certificate you sign off all A1 but not with PIR there will always be points to be raised.

As to second point on voltages you will of course have taken the ELI on these sockets or the meter will have refused to allow you. The problem with a TT supply is that neutral is a live wire and this means of course all RCD's need to be double pole.

Many things can cause the neutral and earth voltages to drift apart and you need to start at the incomer and test the rod to start with. Once the neutral and earth drift over 50v then something needs doing. In fact alarm bells should ring well before that.

It was common to use gas and water as the earth and many houses since the introduction of plastic pipes have lost their earth. I have found houses relying on old party line telephone earths in the past. I have also seen PIR's submitted on a TT system showing an earth resistance of 2 ohms and anyone who sees that will then treat the whole certificate with suspicion. We normally expect once the bonding is removed to see around the 60 ohms mark. For a reading of 8 ohms I had to sink between 3 and 6 times 1.2 meter rods to get 2 ohms I would need to use multi-rods.

I know there are no qualifications required to complete a PIR but to satisfy insurers you do need some way to show your able to do the work. The normal would be a C&G 2391 or if not that clever at least a C&G 2392. You don't seem to have the skill and you do really need to ask ones self if you should be really doing that type of work. At very minimum check your insurance covers. PLI may not you may need PII. At least you have sense to ask.

So is it a TT system and if so what is resistance of earth rod? Also what size RCD's are fitted and of course are they current type. Voltage type have been out for many years.

I find the restriction on leaving a home inhabitable a problem. We are not allowed to remove lighting an heating without ensuring alternative accommodation. So where an installation is dangerous we can't walk away doing nothing but unlike work where one is allowed to countermand the company director in a house you can't just simply switch off until repaired. The Electric supply company has to inform the local authority that the occupants will be homeless before they can turn off the supply which is why pre-payment meters are used.

Hence I shy away from domestic PIR's just too much trouble.
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