Ribbon Underfloor Heating by AHT - Heating

[Uheat]

Thanks for posting the letter from IET.

So, this letter confrims that if the electric ufh is class II then an earth grid is not required unless unless its in a room containing a bath or shower. - Everyone agree?

Now, the next issue that ssheen raised was that an RCD needs an earth to operate. If this is the case, then class II without an earth will not comply with 17th edition because the RCD won't work.

When I went to college many years ago and we studied the workings of an RCD, an earth was not required because it operated on the imbalance of currents running through the live and neutral conductors. If this is not the case anymore then I think we need to see some documentation that proves that an RCD needs the circuits it supplies to have a cpc (earth). Perhaps it is just some RCD's that need an earth, like RCD spurs?

Tilers, if you buy from Underfloor Heating | Electric | Floor Insulation | Uheat you will not have to worry about all the tech talk above because we only supply electric ufh systems that comply with regs, are fully earthed and will work with RCD's.:hurray:

could not have said it better myself.

:hurray::hurray::hurray::hurray:

 

[HowardM]

An RCD is there to monitor for inbalance in supply, some are connected to earth with a white fly lead others don't.

The AC sensing type uses another coil on the toroid which generates a seperate magnetic field, if this rises above a given thresh-hold the RCD will trip.

So I can say not all RCD require an earth.

 

[pjrich]

An RCD is there to monitor for inbalance in supply, some are connected to earth with a white fly lead others don't.

The AC sensing type uses another coil on the toroid which generates a seperate magnetic field, if this rises above a given thresh-hold the RCD will trip.

So I can say not all RCD require an earth.

Thanks for that, just read something similar on another website.

Does this mean that AHT heating mats are only compatible with some RCD's when there is no earth grid install?

 

[HowardM]

If there is an inbalance with or without an earth grid it will be detected, providing the RCD is not faulty, if the floor develops a fault and goes to earth there will still be an inbalance.

The wiring regulations show that you must not count on the RCD as the only form of protection.

There are installers that use RCBO (DC sensing) and inline RCD (AC sensing).

The thing is simply this 753.514 does have a lot of fault testing to carry out when commisioning, now if this is not done by the electrician or a DIYer has a go not knowing the regulations there is trouble to be had with all products.

We have to look at the fact that all products on the UK market have gone through major test with testing houses such as Nemko, Bsi, TUV or the like to say the conform to set standards.

 

[HowardM]

oops double posted ...

What I will add is its not the safety of a product that should be in question as that has already been tested but the competance of the installer,

All products are fit for their own purpose and should that be brought into question by suppliers / distributors / wholesalers

All products should be sold on merit of service, capability, compatability, etc. and since each individual is different and requirements can differ there is scope for all underfloor heating systems in the market place.

 

[ssheen]

Right,
1. Class II does not need an earth
2. Class II does need an RCD
3. An RCD needs an earth to function properly...
So.....Class II needs an earth but it doesn't need to work?! Sorry, but I'm not buying it.

If I was to install a ribbon system, I would cover it with a small screen earth grid and feel a lot more confident about the safety of the system. Simple.
Loopholes don't sit well with me when there's 240V involved.

BTW - I'm not knocking ribbons and agree with Howard, they must be installed properly

 

[HowardM]

3. An RCD needs an earth to function properly...

A DC RCD needs an earth but most installations us an AC RCD, a replacement of the DC sensing RCD is an RCBO so in effect if you have a consumer board with a DC RCD (uncommon) or DC RCBO (becomming common) and you use say a Contactum RDC fused spur yoy now have both measures in place.

Now go one step further with the RCCBO (Residual Current Circuit Breaker with Overload, basically a replacement for MCB)

Where the consumer board is protected by RCCD (residual current operated circuit breaker)

How much protection can you ask for, must confess this is only for new consumer units.

Edit

Another thought, if you have an AC RCD on an earthed system will it work ?? It will but not due to the earth being present as there is no earth on the RCD, it will however detect electricity has gone missing (in laymen terms, god my spelling is crup).

 

[pjrich]

If there is an inbalance with or without an earth grid it will be detected, providing the RCD is not faulty, if the floor develops a fault and goes to earth there will still be an inbalance.

The wiring regulations show that you must not count on the RCD as the only form of protection.

There are installers that use RCBO (DC sensing) and inline RCD (AC sensing).

The thing is simply this 753.514 does have a lot of fault testing to carry out when commisioning, now if this is not done by the electrician or a DIYer has a go not knowing the regulations there is trouble to be had with all products.

We have to look at the fact that all products on the UK market have gone through major test with testing houses such as Nemko, Bsi, TUV or the like to say the conform to set standards.

Agree with everything HowardM has said, especially that electric ufh must be installed correctly and all electrical works/connections done by a qualified electrician.

However, the question was are AHT heating mats only compatible with some RCD's when there is no earth grid installed?

Which, correct me if I'm wrong, has not been answered.

This is important for the tilers on this forum, because if they choose to supply / install a class II underfloor heating for their clients they need to be sure that if the system needs an earth grid when heating installed. Electricians may not be on site when this is done, so can't advise on suitability of existing RCD (if present). Earth grid pretty impossible to retro fit!!!

For the tilers on this forum, a simple yes or no answer would be appropriate to the question, are AHT / Class II heating mats only compatible with some RCD's when there is no earth grid installed?

 

[Uheat]

:dizzy2::dizzy2::dizzy2::dizzy2::dizzy2::dizzy2::dizzy2::dizzy2:

 

[HowardM]

My last statement was slightly untrue

Ref to the RCD with earth, (the old RCD) they have not been used in domestic installations for a long time and are usually 50ma 80ma and 100ma that ar not permitted.

Standard 32ma RCD do not need and earth they have a coil on the live a coil on the neutral then there is a coil between the two, if the polarity on the first two coils differs then the 3rd coil will actuate a trip.

The property and and circuits however do need an earth or be bonded there are exceptions that can be found in BS7671:2008 (the good book)

Also an RCBO is just simply an RCD (standard) with built in MCB (over current protection)

So in answer to your question the AHT system is compatible with All Regulation RCDs with or without an earth grid.

The fact still remains the system is "Double insulated" which means it is harder to damage and expose the live conductor hence the reason it is give CLASS II status.

Also take into account the fabric of the property be earthed and various means of supplimetry bonding.

Please also note that the design purpose of the system is it does not need an earth grid, the fact is Bs7671:2008 and previous requires that in bathrooms a supplimentry earth is installed above and I am happy it is (Helps the Adhesive Key in Nicely).

 

[pjrich]

My last statement was slightly untrue

Ref to the RCD with earth, (the old RCD) they have not been used in domestic installations for a long time and are usually 50ma 80ma and 100ma that ar not permitted.

Standard 32ma RCD do not need and earth they have a coil on the live a coil on the neutral then there is a coil between the two, if the polarity on the first two coils differs then the 3rd coil will actuate a trip.

The property and and circuits however do need an earth or be bonded there are exceptions that can be found in BS7671:2008 (the good book)

Also an RCBO is just simply an RCD (standard) with built in MCB (over current protection)

So in answer to your question the AHT system is compatible with All Regulation RCDs with or without an earth grid.

The fact still remains the AHT system is "Double insulated" which means it is harder to damage and expose the live conductor hence the reason it is give CLASS II status.

Also take into account the fabric of the property be earthed and various means of supplimetry bonding.

Please also not that the design purpose of the AHT system is it does not need an earth grid, the fact is Bs7671:2008 and previous requires that in bathrooms a supplimentry earth is installed above and I am happy it is (Helps the Adhesive Key in Nicely).

Just spoke to a gentleman called Dave, in the technical department at Crabtree (major manufacturer of circuit protection equipment) and he has advise that all their single module RCBO's are supplied with an earth fly lead. These earth leads are typically coloured white or cream, which designates them as functional earths, which means that an earth is required to ensure that the RCD part of the RCBO operates correctly in the event of a fault.

The purpose of the earth fly lead on single module RCBO's is to ensure that the breaker trips in the event of the neutral of the circuit being lost.

The conclusion is that you do require an earth (CPC) for circuits that are connected to RCBO's or RCD's that have an earth fly lead.

Why else would the manufacturer's have the earth fly lead, decoration?

There may also be other RCD's or RCBO's that require the earth to be connected but as yet I have not received any information back from the manufacturer's that I have requested information from.

Therefore, I have to conclude that Class II equipment such as AHT underfloor heating mats are NOT compatible with all RCBO's & RCD's, unless a seperate earth grid is installed over the top of the system.

So, for the Tilers in this forum, you may or may not have to install an earth gird over the heating, it depends on the method of earth leakage protection (RCD / RCBO), if you choose to install an Class II system such as AHT.

Let's make it even easier for the members of the Tiler's Forum, if you buy your underfloor heating from Uheat (Underfloor Heating | Electric | Floor Insulation | Uheat) all the the systems we supply are 100% earthed and you will not have to worry about which RCD / RCBO is installed (let the sparky do that).

Don't forget, as sponsors of the forum, we offer you guys special prices, check out the Tilers Forums Arms or contact Aaron or myself.:smilewinkgrin:

 

[HowardM]

Therefore, I have to conclude that Class II equipment such as AHT underfloor heating mats are NOT compatible with all RCBO's & RCD's, unless a seperate earth grid is installed over the top of the system.

Everybody is entitled to make their own conclusions.

I am now too scared to switch my lights on as they are not protected by RCD nor do they have an earth :yikes:

 

[pjrich]

Everybody is entitled to make their own conclusions.

I am now too scared to switch my lights on as they are not protected by RCD nor do they have an earth :yikes:

My conclusion is based on the fact that the 17th edition of the IEE wiring regs demand that electric underfloor heating are protected by an RCD - FACT

Also, a leading manufacturer, Crabtree, has stated that for their single module RCBO's require an earth on the circuit it supplies to function correctly - FACT

As you have stated AHT mats are CLass II and do NOT have an earth - FACT

Your lights mat have been wired many years ago to the predeceeding regulations, i.e. something like the 13/14th edition or even befireand in those days no earths and RCDs complied with the regulations at the time.

However, we are talking about the current regulations and Tilers doing installations now which have to comply with the current regulations. So your comment about being scared to turn on the lights has nothing to do with the current discussion.

 

[Dan]

Dan,, you make this sound like it is the fault of the product and not the installation. was it damaged during installation? was the earth connected? was there an RCD in place? was it commisioned by a qualified electrician?

People can get electric shocks from all types of electric underfloor heating be it AHT, Devi, Electra if it was not installed incorrectly.

A bit confrontational for a first post but BS7671:2008 and previous would not allow any form of underfloor heating be activated by an electrician if it failed a basic insulation test.

Like I said, I never heard from the lady after passing it onto to AHT, clearly it must have been installation issues. I just didn't like the stuff generally though, and the made claim that it heats up the whole room in three minutes is a bit far out. It would take a fire in the room to do that in my opinion.

 

[Dan]

My last statement was slightly untrue

Classic.

:mad2: