Twin and Earth American style

[Mark Wright]

Can anyone tell me more about Twin and Earth American style?

What's it's full name? NM?
Is it always flat?
Do you add a sheath to the ground/earth cable?
Thanks

 

[nicebutdim]

Only fact I've learned about the stuff is it's commonly known by the brand name 'Romex'.

Google tells me NM stands for non-metallic (sheathed).

Edit: Earth generally left bare according to this fairly informative page.

 

[Dustydazzler]

Pretty much all YOuTube sparks in America and Canada refer to that cable as ROMEX , which I believe is a brand name. It is much harder than pvc twin and earth , it is much more like our LSF cable. Yes the NM stands for Non Metalic.
It comes in a wide variety of gauges much like our twin and earth does where the line and neutral come sheathed and with a bare copper earth / cpc / ground wire.
Yes it is always flat with The main difference being they have a White for Neutral and Black/Very dark grey for Live.
Also from what I can tell you are not allowed to wire Romex surface mounted , it must either be in the fabric of the building Or run in a conduit.
This guy waffles a fair bit and even muddles up his colours but he explains the different sizes , and colours of Romex common in his area

 

[Mark Wright]

Wow thanks really interesting.
I also found this video interesting about the Switch Line/ Switch Leg

 

[Dustydazzler]

American / Canadian terminology for everything is so bizarre, not to mention they can mix lighting and receptacles ( sockets ) on the same circuit and can have receptacles ( sockets ) in bathrooms

also the fact the the bigger the gauge on the wire the smaller it actually is , this had be stumped for ages when watching American YouTube stuff.

 

[Avo Mk8]

also the fact the the bigger the gauge on the wire the smaller it actually is , this had be stumped for ages when watching American YouTube stuff.

That was also the case for British Standard Wire Gauge (SWG). I spent many hours winding coils with enameled copper wire, always referred to by its SWG size, back in the day!

 

[Dustydazzler]

Yes once you actually understand the smaller the gauge the larger the wire it makes sense , but for anyone watching an American vid it must be a head scratcher at first

As the gauge only goes up to 0 , I believe they also have 00 and 000 gauge wire in America because the original SWG doesn't go big enough

 

[Avo Mk8]

Something I didn't know until a moment ago, having looked at Wikipedia, is that SWG continues 'below' 0 as 2/0, 3/0, .... to 7/0, the latter being 1/2 inch diameter. Now that is confusing - sounds like it should be the number of strands of 0 gauge wire!

Standard wire gauge - Wikipedia

en.wikipedia.org

 

[Dustydazzler]

Yes I certainly heard it referred to 00 , 000 wire in American Vids, rather than 2/0 3/0 , but I guess it means the exact same thing

 

[Mark Wright]

Was UK T+E ever in imperial sizes? If so what was for example 2.5mm

 

[Lucien Nunes]

they can mix lighting and receptacles ( sockets ) on the same circuit

This is normal nearly everywhere except UK. Our need to strictly separate lighting and sockets comes mainly from our use of 32A circuits which in turn comes from fused plugs. We used to be able to put lights and 5A sockets on the same circuit (and still do, for controlled lighting sockets) but 32A (or 30A as it was originally) is too big to mix with lighting.

for anyone watching an American vid it must be a head scratcher at first

We used to use gauge numbers for British wiring cables too, obviously SWG rather than AWG, before we went to the strand diameter in inches. So the cable we remember as 3/.029 started life as 3/22 - likewise it's not a fraction but the number of strands and the SWG separated by an oblique. I have a number of early British electrical books that reference cables sizes in this way. Many of the fractional inch sizes are equivalent to SWG: .036" = 20SWG, .064" = 16SWG. Some aren't, 0.044 wasn't an SWG size IIRC. Although the principles of AWG and SWG sizing are the same, the actual dimensions differ.

Main differences of USA NM from UK T+E:

• Ground conductor is same size as others
• Core insulation is 2-layer, PVC has a skin
• NM-B is 90 degree rated, and is now standard
• Sheath of newer cables is colour coded to identify size
• Size quoted in the form 12-2 where 12 is the AWG and 2 the number of cores other than ground
• Colours W & B / W, B & R

 

[Dustydazzler]

Was UK T+E ever in imperial sizes? If so what was for example 2.5mm

That is one for the OGs on here to tell you about , but in a nut shell yes pre modern T&E there was a stranded flat cable with pvc sheath and before that a rubber sheath that came in various gauges

 

[Lucien Nunes]

Was UK T+E ever in imperial sizes? If so what was for example 2.5mm

Indeed, it was imperial for longer than it has been metric. Until 1966 not all flat cables had an earth core, they were called flat twin, flat triple, flat twin & earth etc. The same sizes were usually available in lead-sheathed or rubber-sheathed as desired, up to the introduction of PE and PVC insulated. The conductors of imperial-sized cables are usually tinned copper rather than plain.

First, as I mentioned above, it was in SWG sizes. The conductors were quoted as the number of strands and their SWG, for example 7/22 (which is not a fraction) meant seven strands of 22 SWG.
Then we switched to identifying the strand size by diameter in inches, so 7/22 became 7/.029 (note position of dot and zero)
That was the nearest to 2.5 sqmm, actually nearer 2.9
Normal lighting circuits were wired either in 1/.044 which is like 1.0 sqmm, or the larger and more flexible three-strand 3/.029.
Next up was 3/.036 and 7/.029 for sockets. 7/.044 was about the largest regularly used as flat twin or twin & earth, above which it tended to be singles in conduit.

The odd one out was imperial MI, for which the conductors were always sized in sq. ins. instead off ins. diameter, although the cable sheath was sized as ins dia.

 

[westward10]

The row of houses I live in were built in 1970. Mine has metric cables but go to the top of the road they are imperial, this was roughly the change over period so they must have been using their old stock.

 

[Mark Wright]

Going off-topic again I was doing a job lately and there was some silk? covered cables in very old conduit. The conduit was in great condition it was black. Could still use it really and the cable wasn't in bad condition really. Don't worry it wasn't actually in use. Just under the boards.

I wanted to post a pick on here but think someone chucked it.

 

[Lucien Nunes]

Unlikely to be silk, which was only used for very fine coil winding wires due to cost. Before PVC, the normal insulation for British conduit cables was VIR, vulcanised rubber covered with an impregnated cotton braid. The rubber provided the insulation, the cotton provided the strength and abrasion resistance, and the impregnation protected it against rot. Other woven coverings for power cables included polybutyl jute and cambric.

 

[Mark Wright]

Thanks. I'll see if I have some pictures but I don't think there was any rubber so I suppose it could of just perished?

 

[Mark Wright]

Probably does have rubber. So annoying had some put aside to look at closer and think it's been binned.
Here's a picture not great.

 

[Lucien Nunes]

That's ordinary VIR conduit cable, I can't see the conductor to say what size it is. Rubber extruded over the conductor (sometimes in two layers) and the braided cotton serving over the top. There's thousands of miles of this stuff still in use, decreasing rapidly now but not all gone yet. The same is true of the nearest USA equivalent. They used a version with a heavier cotton braid but basically the same concept.

When the rubber-insulated cores were used inside a rubber or lead sheath, instead of the woven cotton braid they were usually lapped in cotton tape.

 

[Megawatt]

Can anyone tell me more about Twin and Earth American style?

View attachment 107858
What's it's full name? NM?
Is it always flat?
Do you add a sheath to the ground/earth cable?
Thanks

NM or Romex is flat for 14/2, 12/2, or 10/2 or 3 conductor. Starting at # 8 or # 6 is normally round. I still can’t understand why we have naked grounds but it’s easy to purchase shrink tubing that can be installed on the naked wire. Be sure and mark it green.