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External Oil Fired Central Heating Boilers


Revved Up Sparky

Question

I have'nt wired one of these for a while. Any input gratefully received. Thanks !.

Main Equipotential Bonding

The incoming oil service never enters the house and the plastic lagged pipework is clipped on the surface from the oil storage tank a few metres away. Do you think I am right in thinking the oil service does not need a 10mm MEBC clamping onto it ?. The pipe is not buried therefore it cannot bring earth potential into the house via the heating pipework.

Isolation and Switching

If such a boiler is outside, does it always need an external isolator ?. I have'nt got the regs in front of me so I have'nt looked it up yet but I reckon it should have an external isolator for safe and accessible isolation with some copex going into the unit to provide mechanical protection to the load flex.

Three lives ?

This particular unit (a combi) seems (from manufacturers info) to need three lives !, a permanent live, then two switched lives for DHW and CH. I thought a permanent live for DHW and switched live for CH would suffice but it seems this unit has a small storage tank in it so I am thinking it needs the perm live to keep enough DHW hot for a few sinkfuls but the DHW live to call for more.

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5 answers to this question

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i raised a few questions about external boilers on my annual inspection as i was a bit worried about exporting earths to metal tanks.

this is how i look upon it, if the oil line doesnt enter the property it is not bonded as it is not a incoming service. pipework will be earthed through the boiler in all the cases i have come across.

i just use spurs that can be locked in the off position to avoid using external ip rated isolators which are not pretty. the boiler will have a isolation switch for servicing and such like.

as for the three lives i would just follow the manufactures instructions, all the boilers i have been involved with are heat only so cannot comment.

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Thanks Wozz. I appreciate you taking the time to comment. :O)

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I have'nt wired one of these for a while. Any input gratefully received. Thanks !.

Main Equipotential Bonding

The incoming oil service never enters the house and the plastic lagged pipework is clipped on the surface from the oil storage tank a few metres away. Do you think I am right in thinking the oil service does not need a 10mm MEBC clamping onto it ?. The pipe is not buried therefore it cannot bring earth potential into the house via the heating pipework.do a resistance test between pipework an earth. if its under 22K ohms, earth it. just because the pipework isnt buried, doesnt mean it cant introduce a potential. its probably going to be indirectly in contact with ground through the boiler

Isolation and Switching

If such a boiler is outside, does it always need an external isolator ?. I have'nt got the regs in front of me so I have'nt looked it up yet but I reckon it should have an external isolator for safe and accessible isolation with some copex going into the unit to provide mechanical protection to the load flex.

you should have an external isolator (unless internal can be locked)

Three lives ?

This particular unit (a combi) seems (from manufacturers info) to need three lives !, a permanent live, then two switched lives for DHW and CH. I thought a permanent live for DHW and switched live for CH would suffice but it seems this unit has a small storage tank in it so I am thinking it needs the perm live to keep enough DHW hot for a few sinkfuls but the DHW live to call for more.there should be one point of isolation, so you could have one main switch inside and a 3 (or 4) pole rotary isolator outside which will cut all 3 lives. or you could use a DP switch inside that can be locked, and then go through the controls and to the boiler (but i would still recommend an external isolator)

my red

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....do a resistance test between pipework an earth. if its under 22K , earth it.

Thanks Andy. Which earth ? the general mass (via a test rod) ? or the MET ?

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pipework and MET

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