“Domestic” Cable for Motor Applications

[IAmSparkytus!]

Good afternoon all,

First time posting on here so not sure if this is the correct place to post this but I’m sure you will all correct me if it isn’t.

My query today is whether anyone can see a problem using twin and earth to supply motor units fed from C rated MCBs?

I have enquired with an NICEIC assessor who says he doesn’t see the problem with it but still remain unsure and uncertain within my head.

Maybe this is unacceptable in all circumstances, maybe it’s ok for shorter runs but not larger runs, could be that it’s perfectly fine.

Please let me know your thoughts! Thanks.

 

[AJshep]

So the T&E terminates into the rotary Isolators. What cable have they used from the rotary isolator ?
I'd be more interested In disconnection times, what size are the motors ? are the motors incorperated into a pre-wired unit or are they independantly switched on via the Rotary isolator ?
552.1.2

 

[IAmSparkytus!]

I would like to know out of curiosity, westward10 - is that unheard of? Might be useful information in the future you never know.

And i’m not sure, just didn’t seem like it was good practice for some reason in my head. Can’t put a finger on it.

 

[westward10]

Thought you might be doing an EICR. What are the final connections done with.

 

[AJshep]

Oh I just assumed the OP was doing an EICR

 

[Risteard]

Aside from the responses above saying about vibration on the motor terminals, why did you think it was not suitable to use? What exactly is "domestic" cable?

To be fair T&E type cable is domestic cable. It's really not designed for non-domestic use. Such use might be described as "value engineering".

 

[Dillb]

To be fair T&E type cable is domestic cable. It's really not designed for non-domestic use. Such use might be described as "value engineering".

Really? I have seen it used in many commercial and industrial installs.

 

[Risteard]

Really? I have seen it used in many commercial and industrial installs.

Value engineered ones.

 

[Dillb]

Value engineered ones.

No just ones where it is suitable for the enviroment installed in.

 

[Risteard]

No just ones where it is suitable for the enviroment installed in.

LOL. T&E cable standards specify it as a domestic cable. I will never accept that it has a place in non-domestic installation.

 

[Dillb]

LOL. T&E cable standards specify it as a domestic cable.

Wheres that then? Any BS standards mention it?

 

[Cadgey123]

You see that white LSF T & E lashed in Commercial projects all over the place.

 

[AJshep]

I'm not sure BS 6004 6242y twin and Earth is specified as domestic cable. But you definitely would usually expect to see it more in domestic settings.
Just like the low smoke version BS 7211 6242b you would usally expect to see more in a public building or commercial type setting.

Both are recognised in the BS7671 as technically better than YY SY cable that are non standard.

 

[Marvo]

We have stock of big sizes of twin and earth up to 25mm sq. From memory it's a single solid conductor up to 16mm sq, after that it has multistranded conductors sao maybe the solid conductor sizes are classed as domestic and the larger multistranded sizes are commercial. I think it might actually be available in sizes even larger than 25mm sq as well.

If the motors are run by inverters or drives or any kind of high frequency modulated supply you should avoid using solid conductor cables.

One limitation with twin and earth can be achieving disconnect times with the undersized CPC. Maybe that's why they class it as a domestic cable in the UK because with longer runs and higher potential fault currents in commercial installations it would certainly be a limiting factor.

 

[IAmSparkytus!]

I would like to know out of curiosity, westward10 - is that unheard of? Might be useful information in the future you never know.

And i’m not sure, just didn’t seem like it was good practice for some reason in my head. Can’t put a finger on it.

 

[IAmSparkytus!]

Each motor unit can be switched on and isolated by the rotary isolator adjacent to it.

Units are connected to the isolators by T&E cable as well.

No solid answers so far as to why it would be a bad idea to use twin and earth other than the install not looking as good as it maybe could have done.