“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.

 

[suffolkspark]

Solid cores into a unit which is subject to vibration? And it will look rough as old bulls ears. Terminate the t/e locally and use an appropriate flex onto the motor

 

[westward10]

Provided it is suited by the installation method it should be fine. I would not use it for the final motor connection though.

 

[Strima]

All depends on the installation method and external influences.

Also how is the motor connected?

Is the cable and termination subject to vibration etc?

Need more info really.

 

[Squid]

When I used to wire motors up in the past it was a connection to a 4x4 box then either a copper or flex from the box to the motor as mentioned above its the vibrations as some motors sit on heavy duty rubber shock absorbers more info needed as then better advice can be given.

 

[Pete999]

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.

Will that be single phase motors or three phase motors, solid core condctorsare not ideal for machines that are subject to vibration

 

[IAmSparkytus!]

In this instance there are 10 motor units positioned throughout a service duct which runs around the perimeter of a building.

The cables are grouped and tie wrapped to a cable tray, go into individual rotary isolators, and then into the units.

Cable runs range from 10-90 metres from the distribution board.

 

[IAmSparkytus!]

Will that be single phase motors or three phase motors, solid core condctorsare not ideal for machines that are subject to vibration

Single phase.

 

[westward10]

What are you using for the final connection.

 

[suffolkspark]

Is this already installed or are you installing? Is this perimeter run internal or external to the building?

 

[Pete999]

Solid cores into a unit which is subject to vibration? And it will look rough as old bulls ears. Terminate the t/e locally and use an appropriate flex onto the motor

 

[IAmSparkytus!]

Is this already installed or are you installing? Is this perimeter run internal or external to the building?

This is an existing installation I have come across. The service corridor is internal with no chance of the weather affecting it.

Usual procedure for myself would be to install using SWA or NYY.

 

[Dillb]

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?

 

[Pete999]

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?

I'm sure the DI brigade will be able to help.

 

[westward10]

So why do you want to know if it is existing?

 

[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.

 

[Rpa07]

Disconnection times referring to the undersized CPC in T +E.
Vibration issues in terminations of the final length Rotary to Motor control are the answers picked up from the responses so far.
A J - disconnect times
Marvo - undersized CPC
Everyone else - vibration issue

 

[Pete999]

Disconnection times referring to the undersized CPC in T +E.
Vibration issues in terminations of the final length Rotary to Motor control are the answers picked up from the responses so far.
A J - disconnect times
Marvo - undersized CPC
Everyone else - vibration issue

With regards to Vibration issues, I was one of those who supported that, but what about MICC that had solid core conductors, although Electricians sometimeput a loop in the cable to counter act vibration.

 

[IAmSparkytus!]

No problem with disconnection times and the earths all seem suitably sized. 6mm twin and earth is the largest in place. There has been 2 x 10mm SY cables installed as well where the earth is obviously the same size as the line conductor.

Regarding the vibration issue, unless I’m missing something or not thinking fully, what difference would a stranded core cable make to a solid core cable if both had a nice tight connection? Or is it not the cable coming loose which you are getting at?

Thanks.

 

[Dillb]

The name flexible cable will be the clue here, seeing as the motors will be vibrating a solid core cable is more liable to snap in the termination than a flexible one.

 

[IAmSparkytus!]

Excuse me if I’m being ignorant but what makes you think a solid core cable will snap with a bit of vibration unless the copper had been nicked or damaged?

 

[Pete999]

Excuse me if I’m being ignorant but what makes you think a solid core cable will snap with a bit of vibration unless the copper had been nicked or damaged?

Something that is of solid construction, is more prone to breakages than something that is flexible, especially solid conductors.

 

[westward10]

Any chance of knowing what cable is used for the final connection.

 

[Pete999]

Any chance of knowing what cable is used for the final connection.

Any chance of knowing what cable is used for the final connection.

Post#30 says the same cable as the supply is used to make the final connection

 

[westward10]

So it does Pete I missed that. More to this than meets the eye me thinks.

 

[Pete999]

So it does Pete I missed that. More to this than meets the eye me thinks.

Thinking the same Westy

 

[IAmSparkytus!]

So it does Pete I missed that. More to this than meets the eye me thinks.

Such as...? I’m happy to give any more information required if it helps.

Thanks.

 

[Rosco]

What’s your opinion on the situation @ToonSparky?

 

[AJshep]

So Rotary isolator directly feeds and operates the motor, or is it some kind of unit with a motor incorperated ?
What size are the motors ?
Are they above 0.37kw ?
Any overload protection provided for the motors ?

 

[Pete999]

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.

Using Twin and cpcfor this type of installation, is not the best Idea in the World.
Using Twin and cpcwill give you a reduced cpc size, then you will have the added problem with solid conductors which people have already commented on, what sort of cable entry are you intending to use, when terminating the twin and cpc? what does your experience and qualifications tell you about using this cable and this installation method? in my opinion asking the NICEIC help desk is like phoning up the Gas board to ask about a water leak, ie a waste of time. Apart from that it wont look very professional, imo.

 

[IAmSparkytus!]

What’s your opinion on the situation @ToonSparky?

As I have said above, I personally use SWA in this sort of installation.
I’m merely asking out of curiosity to see if there was anyone on this forum who would agree that it is fine to carry out the works in this way.
Agreed that I have asked the NICEIC about things in the past and they have come back with “we can’t advise you on that” to which I thought how can you be an assessor yet not give advice. Strange.
In this case however, the NIC bloke said it was fine to do which made me wonder other peoples thoughts on it.

Thanks.

 

[Pete999]

As I have said above, I personally use SWA in this sort of installation.
I’m merely asking out of curiosity to see if there was anyone on this forum who would agree that it is fine to carry out the works in this way.
Agreed that I have asked the NICEIC about things in the past and they have come back with “we can’t advise you on that” to which I thought how can you be an assessor yet not give advice. Strange.
In this case however, the NIC bloke said it was fine to do which made me wonder other peoples thoughts on it.

Thanks.

In that case not something I would do.

 

[Dillb]

Your response about asking the NIC several things im the past and about design aspects looks like you dont have the knowledge to be carrying out electrical works in the enviromnets that you are working in. Surely they are only used to seek reassurance or to clarify a grey area of which there are alot of in BS7671.

 

[westward10]

It seems odd that if you just curious you have gone to the effort of contacting the NICEIC.

 

[IAmSparkytus!]

It seems odd that if you just curious you have gone to the effort of contacting the NICEIC.

Always good to ask questions on things you are unsure about. No harm in asking is there? Feel it would be wrong to advise a customer about things like this in the future unless I’m sure myself.

Your response about asking the NIC several things im the past and about design aspects looks like you dont have the knowledge to be carrying out electrical works in the enviromnets that you are working in. Surely they are only used to seek reassurance or to clarify a grey area of which there are alot of in BS7671.

I didn’t say I had asked about “several things” so please don’t put words in my mouth in what seemed to be an attempt to belittle me. The past couple of questions I have asked them about were regarding JIB cards and ECS assessments so completely unrelated.

Thanks.

 

[Dillb]

The past couple of questions I have asked them about were regarding JIB cards and ECS assessments so completely unrelated.

Thanks.

Its no wonder they cant help you when you ask them about things they having nothing to do with.