Domestic extension to Ring Final - Earth Bonding to Services advice

[freedomrun]

TN-S Domestic, 30mA RCD, 32A MCB, 2.5mm T&E I've been asked to install some socket outlets and connect up previously installed underfloor electric heating (2400W) plus some wall lights in a Conservatory project that got built, but electrical works not completed by the the time the building firm used at this property became bankrupt. It looks like all the wiring is in place ready to go and the underfloor heating is installed. I'm going to extend the ring at a socket outlet to accomodate the additional circuit and load - and will use a FCU to connect the Underfloor heating to the Ring via it's controller, same with the lights for this extension (via FCU). Doing my initial checks i have found that the property has no Bonding to the Gas or water, i've informed the customer that this should be addressed, but they do not want to have this installed - shall i just note this on my EIC when i complete the work i've been asked to do. Also - I've not had anything to do with electric underfloor heating before, anything (Testing wise) i should consider maybe, it's basically just an element like in an immersion heater i guess? Cheers.

 

[jayonwheels]

I'd just issue a danger notification and make sure they sign a copy for proof of acknoledgement regarding the lack of main gas / water bonding. I used to get alot of those kind of jobs, finishing other firms work and my main concern has always been keeping the NIC man happy.

 

[davie spark]

If I was you I'd run a separate circuit for the floor heating and advise the customer that you cannot satisfactorily complete certification to confirm a safe installation without the main bonding being installed. Offer the client a price for installing bonding and point out the dangers at the same time but also be sure the client understands you are not trying to frighten him/her into having the work done, rather it's a requirement.

 

[steve-the-hat]

Are you sure you want to take this on? If the householder doesn't want the bonding done then personally I would walk away.

Electric underfloor heating is nothing like an immersion heater and needs to be on its own circuit.

 

[Octopus]

IMHO no bonding, no additional electrickery to be done.

I'd be giving the customer a copy of the ESC leaflet covering this very subject.

 

[richy3333]

Personally I'd walk away too. The bonding should be done and unless the underfloor heating is tiny then surely it will need a separate circuit. What do the installation instructions say? The ones I've installed the customer has given me an additional form to fill in for the guarantee - think it asked for continuity/IR results?

 

[Deleted member 26818]

Is the under floor heating in the bathroom, or the conservatory?

 

[Knobhead]

This puzzles me, if a DNO can make a connection to a dodgy system by getting the customer to sign a disclaimer why can’t an electrician?

Disclaimer 2 on page 15 http://www.sppowersystems.co.uk/newconnections/pdf/EART-01-002%20Issue%203%20-%20Low%20Voltage%20Earthing%20Policy%20and%20Appl..pdf

 

[telectrix]

probably because your average electrician doesn't have an army of high priced lawyers on call who are paid for with DNO funding.

 

[freedomrun]

The underfloor heating is under the nice new tiled floor of the conservatory, the area of the heating element is 12m squared and the rated power consumption is 2400W - so i work out the current pull to be about 10.5 Amps. Would using a FCU to connect this load to the RFC not be an option - many domestic kitchen ovens now come with a 13 AMP plug top and they are rated at 2-2.5KW these are designed to be used without the use of additional overload protection other than the 13A Fuse - can this underfloor heating rated at 2400W be considered the same? Or should i consider this similar to an Immersion heater install which is not permitted by the regs anymore as it's too much load on one part of the RFC - if this is the case what reg relates to this and underfloor heating directly?

 

[richy3333]

Well there's no Reg I'm aware of that specifically relates to underfloor heating?? but at 2.4KW I think you should be placing this on it's own circuit?

 

[GaryM]

The underfloor heating is under the nice new tiled floor of the conservatory, the area of the heating element is 12m squared and the rated power consumption is 2400W - so i work out the current pull to be about 10.5 Amps. Would using a FCU to connect this load to the RFC not be an option - many domestic kitchen ovens now come with a 13 AMP plug top and they are rated at 2-2.5KW these are designed to be used without the use of additional overload protection other than the 13A Fuse - can this underfloor heating rated at 2400W be considered the same? Or should i consider this similar to an Immersion heater install which is not permitted by the regs anymore as it's too much load on one part of the RFC - if this is the case what reg relates to this and underfloor heating directly?

From Appendix 15

1 RING FINAL CIRCUIT ARRANGEMENTS, REGULATION 433.1.5

The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers). This can generally be achieved by:

(i) locating socket-outlets to provide reasonable sharing of the load around the ring
(ii) not supplying immersion heaters, comprehensive electric space heating or loads of a similar profile from the ring circuit
(iii) connecting cookers, ovens and hobs with a rated power exceeding 2 kW on their own dedicated radial circuit
(iv) taking account of the total floor area being served. (As a rule of thumb, a limit of 100m2 has been adopted.)

Also, have a read of section 753 for an idea of the information required for documentation.

 

[MarkieSparkie]

Well there's no Reg I'm aware of that specifically relates to underfloor heating?? but at 2.4KW I think you should be placing this on it's own circuit?

Oh really! There is only a whole section in Special Locations 753 Floor and Ceiling Heating Systems. Also, paraphrasing Appendix 15 A RFC should not be used to supply comprehensive electric space heating systems.