Whats All This Stuff Regarding 1mm T + E?

Hi JP

The issue is being blown out of all proportion by one particular contributor.

Lighting circuits (bearing in mind loading) - however stuff might change with florries in the equation.

No problem wiring in 1.0mm if protected by 6A breaker. 1.0mm rated approx 11 amps derated according to conditions.

Lighting circuits with smokes/co's on the principals.

As above

Boilers no

Would not see this as an issue based as above, however larger boiler and pump 1.5mm due to motor.

Smokes/co's on a dedicated (but who the heck would do that)

Smokes and co's take less than lights so no problem to me if they are 1.0mm according to conditions and on 6A breaker

Bell transformers

As above. 1 bell transformer on its own circuit in anything bigger than 1.0mm? Why? Nonsense!.

Dedicated burglar alarm circuits

Based on calculation, probably a 1.5mm feed, but for a small system taking something that a 3A fuse would protect I wouldnt have an issue.

Arc welders no

Who has an arc welder in the house? It would be at least a 13A plug or otherwise requie a dedicated 16 or 32A supply.

What matters is proper circuit design. The circuit must be designed to operate in the environment it is to be installed in, handle the current it is expected to be required to and to be appropriate for the conditions it is to be subject to.

For example a circuit to supply smokes and co's in a freezer room wired in 1.5mm t & e cable not taking the extremes of temperature into account is totally inappropriate.

The Regulations state many things, but to comply properly common sense and calculation need to be employed. Taking the issue you quoted as being literal is asking for trouble. System and circuit design are the important factors and ensuring the circuits and cables are appropriate for the environment and conditions.

I hope this helps and makes sense.

Kind regards

 

My opinon JP. Others - including the one - may disagree. But I would be happy to defend what I have stated.

Kind regards

 

Good reply with most lighting circuits some where having items rated at 6 amp it is hard to every use the full 16A max of the regulations so in real terms most lighting circuits due to some where using a ceiling rose as a junction box are limited to 6A. One needs over 29 meters of cable before we get a problem. However 29 meters is not that long really. Wired rose to rose unlikely ever exceeded but wired switch to switch then maybe.

I am like I am sure many others guilty of forgetting the volt drop requirements. If we assume the 6 amp is even over the length of the run then 58 meters using 1.5 lifts us to 44 and 88 meters I question if really likely we ever use that much cable in a lighting circuit.

So should we be measuring the loop impedance to work out volt drop? I know regs say 6.9 volt, but with LED lamps they will often work with full output down to 150 volt. So why worry about volt drop?

 

When I served my apprenticeship back in the early 70's the rule of thumb was 10 lights wired in 1.0mm based on 100 watt bulbs. Given that not all lights had 100 watt bulbs fitted you could get away with an extra one or two. There were no fancy fittings with halogens and things, it was bulbs or fluorescent fittings.

I can see with the advent of light fittings with 4 or 5 halogens rated at 50 watts each or recessed lights where there are say 10 or more fitings in a room this not longer holds.

As we move to LED lights that require very little current to operate and get away from the heat generators 1.0mm becomes acceptable again.

Volt drop is dependent on the design current for the circuit. If the expected load drops through the use of more efficient light fitings the volt drop will be much less and as stated by MGW the tolerance of modern fittings is much wider.

 

The overall point being that you can pretty much ignore table 53 or what ever it was that said only use 1mm for lighting ctts. It seems it just a European requirement that was put in to satisfy the need for harmonization.

 

I have found it more practical to avoid labelling a circuit, or more accurately, giving a circuit a name. If you design a 6A circuit it can be used appropriately for whatever accessories deemed suitable, same as a 16A radial, 20A radial etc etc. The circuit is designed for a typical load. When it comes to labelling the circuits on the CU then the label just identifies what the circuit has been used for. Looking at the flipside it doesn't mean that once a circuit has been labelled it can't be changed to use it for something else. If you had two 1.0mm2 6A circuits side-by-side in a CU, one serving lights and one serving smoke detectors there is no plausible reason that you couldn't swap them around. Better then, IMHO, to think of a circuit as one which is designed to supply a particular load rather than what is on it/what it is being used for. The user would see that if a socket doesn't work and there is a mcb tripped on the CU marked as sockets then that would correspond. Anyway you get my drift.

 

And always remember the regs. are not statutory. If we designed a circuit to be protected by a 6 amp type B mcb with 1mm t/e we can in theory put what we like on it, we'd just have to be willing to stand-up in court to justify our actions if something drastic happened in the future!

 

Doesn't matter whether the Regulations are Statutory.
If you sign and issue a Certificate stating that you have complied with the requirements of BS7671, when in fact you haven't, you could be liable for fraud.

 

Anyone with any sense would enter it as a departure from 7671 on the cert. wouldn't they?

 

Too simple.

 

Sounds a bit of an ott statement to me tbh mate.

 

Could do that, or you could just use 1.5mm.

 

Or you could use 1mm and accept that it DOES comply with 7671 even if it's not on lights.

 

Unfortunately now we have table 53, using 1mm would not comply.
Is my statement over the top?
In this day and age with all the litigation that's flying about, do you really want to take the risk that someone may decide you have committed fraud or produced a false instrument?

 

What an irresponsible attitude to take spin. Fraud. What a bloody *** . Classic example of a person who has no conception of reality. I really wish bigoted idiots like spin would do something else. Fraud my fn ****.