mm2 ampacity restrictions

[Gardner]

Under BS7671, what is the amperage of 1.5mm2, 2.5mm2 and 4mm2 copper conductor restricted to when inside a race way or cable of no more than 3 current carry conductors? Thank you! :smiley2:

 

[Gardner]

A couple ot three comments in no particular order.

Wire nuts went under the name "Scruit" not screwit - that's a whole different thing. Particularly if you spell whole incorrectly. Scruit was/is a trade name IIRC.

RS Components and others still supply them.

As far as I can tell, they are not illegal in UK. I see nothing in BS7671 that proscribes their use

No, I haven't seen them used in at least 40 years. In any case, the need for them has largely gone away. Fittings have screw terminals on which to land conductors that just need to be connected together.

And the mention of amperage (a horrid non-word IMHO) in the opening post was a pretty good clue that the poster was American. Yank? Maybe not. That would depend on which side of the Mason-Dixon line he's from.

My sweet Southern Belle would be quite offended, horrified even, to be called a Yank.

Wire nuts when done right are a none issue. I have seen very few if any properly terminated wire nuts fail. In fact I have seen other connections fail much more frequently. And I have opened many electrical boxes/panels hunting for faults that say so. Of course our wire gauges are larger, and our wire nuts might be differently designed than those overseas, so the breaking mentioned or burning up is rarely seen here. The biggest issue if I had to pick is actually back stabbed outlets/switches which are unfortunately still legal under UL and the NEC yet burn up like no tomorrow. Any service electrician will tell you.

As for the high number of electrical fires in the US it boils down to two things: Hack work and the way fires are reported. Hack work is a huge issue in the US (work done by none qualified personnel). Material can be obtained from large home improvement stores no questions asked. In most places Home owners can legally do electrical (even if they have no clue what they are doing), and even where permits are required, those doing the work do not always always pull them. Handy man specials are the same thing. Scary, freaky code violations and no way to crack down on them.

When a fire does happen determining the origin can be difficult. Once arson is ruled out, its guess work. More often than not Fire Investigators will just go ahead and assume the fire is electrical and thats what gets written down. As a result certain fires (like electrical fires) get over reported.

 

[Lucien Nunes]

It's possible to make a sound connection with wirenuts but also possible to make a poor one that looks OK. This can happen for many reasons, competence, working conditions, working under pressure, mechanical disturbance etc. With a cage clamp or live-spring action, it's almost impossible to make a connection that looks OK but isn't, or one that will fall apart when the cables are wriggled. I.e. if the cable goes in and doesn't fall back out, it's almost certainly an excellent connection up to and over the cable capacity. So these types of connector, although slightly more expensive, take some of the variables out of the equation. In the real world, where people will be making connections under all kinds of circumstances, the certainty of action is worth this. They are also faster, which might pay for the difference.

 

[DPG]

origional poster
forget posting here
go to an american site

He needs to know British requirements - read his posts! Daz

 

[rapparee]

And the mention of amperage (a horrid non-word IMHO) in the opening post was a pretty good clue that the poster was American. Yank? Maybe not. That would depend on which side of the Mason-Dixon line he's from.

My sweet Southern Belle would be quite offended, horrified even, to be called a Yank.

Apologies to the potential redneck johnny reb, if he is from the south ... long live the confederacy and the south shall rise again etc etc

 

[Gardner]

Apologies to the potential redneck johnny reb, if he is from the south ... long live the confederacy and the south shall rise again etc etc

No offense taken I am actually up from the North, but even if I was in the South, I wouldn't still wouldn't take it personally. :cool4:

 

[Engineer54]

A couple ot three comments in no particular order.

Wire nuts went under the name "Scruit" not screwit - that's a whole different thing. Particularly if you spell whole incorrectly. Scruit was/is a trade name IIRC.

RS Components and others still supply them.

As far as I can tell, they are not illegal in UK. I see nothing in BS7671 that proscribes their use

No, I haven't seen them used in at least 40 years. In any case, the need for them has largely gone away. Fittings have screw terminals on which to land conductors that just need to be connected together.

And the mention of amperage (a horrid non-word IMHO) in the opening post was a pretty good clue that the poster was American. Yank? Maybe not. That would depend on which side of the Mason-Dixon line he's from.

My sweet Southern Belle would be quite offended, horrified even, to be called a Yank.

Firstly, No-one said anything about wire nuts being ''illegal'', but i don't allow there use on any of my projects!! Secondly What does it matter if i spelt Scruit incorrectly?? Lastly wire-nuts may still be available at RS and other wholesalers but like you say, very few have seen them used on UK installations for around 40 years, ...So i'll rest my case there!! lol!!

 

[Gardner]

Table 4D2A – Multicore 70c thermoplastic insulated & thermoplastic sheathed cables (e.g. PVC T&E), non-armoured.* All values assume an ambient temperature of 30c and a conductor operating temperature of 70c.*


Im assuming reference method a


1.5mm = 14A

2.5mm = 18.5A

4mm = 25A

In regards to the final outcome, when a none standard current carrying capacity comes up, is the OCPD (circuit breaker rating) rounded up or down? An example, if 2.5 comes at 17amps factoring insulation restrictions (method used), would the RCBO be 16amps or 20amps?

It may seem silly but in the NEC we have a next size up rule. If the wire comes up at a none standard breaker rating we can jump to the next common size up. IE, our number 6 copper Romex comes out at 55amps, but we can legally put it on a 60amp breaker.

 

[davesparks]

Our calculations work a bit differently to that,

We select an OCPD rating based on the load to be supplied, then apply correction factors for temperature, insulation, grouping etc to that, then the result of that calculation is used to select cable size.

The cable selected will be whatever has a rating equal to or higher than that calculated value.

After that voltage drop, CPC size and earth fault loop impedance calculations are carried out to ensure compliance with those rules.

The exception to the rule is a fixed load which by its nature is not subject to overload, on this case the cable size calculation is based on the actual load and not the OCPD rating.

 

[Knobhead]

Screwits or Wirenuts, whatever you want to call them were banned by our company during the 2[SUP]nd[/SUP] year of my apprenticeship. I’ll leave it to you to work how long ago that was.

Years later a rep tried to convince me how good the new version was, he got shown the door.

If the septic’s want to use them it’s their choice. Don’t inflict them on us.

 

[Knobhead]

My sweet Southern Belle would be quite offended, horrified even, to be called a Yank.

My ex GF had no objection to me calling her a septic.

 

[Gardner]

Our calculations work a bit differently to that,

We select an OCPD rating based on the load to be supplied, then apply correction factors for temperature, insulation, grouping etc to that, then the result of that calculation is used to select cable size.

The cable selected will be whatever has a rating equal to or higher than that calculated value.

After that voltage drop, CPC size and earth fault loop impedance calculations are carried out to ensure compliance with those rules.

The exception to the rule is a fixed load which by its nature is not subject to overload, on this case the cable size calculation is based on the actual load and not the OCPD rating.

Thanks! By chance do you have the BS7671 article number or numbers? I will read up on them.

 

[Knobhead]

I have to wade through the NEC with no help, you can do the same for BS7671.

 

[Gardner]

In regards to earth loop impedance, this is just to make sure the continuity of the earth conductor is UN-interrupted? My understanding is that the Active and Neutral is shorted to ground at the furthest socket on the circuit and a measurement is taken between the Active and Neutral across to the Earth conductor from that circuit? Active, Neutral and earth are all disconnected from respected terminals at the consumer unit during this test as well as making sure nothing is plugged in.

 

[Gardner]

I have to wade through the NEC with no help, you can do the same for BS7671.

What would you like to know?

 

[Knobhead]

What would you like to know?

Once you know how to cross reference an index BS7671, INEC and NEC cause me no problems.