“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.

 

[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.

 

[Pete999]

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.



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.

I don't think anyone is trying to belittle you Mate, it just seems odd that with your quals and experience you are asking questions that you should be aware of.

 

[AJshep]

It does sound like a strange install, ToonSparky.

It's not how I would install it anyway.
Anyway you didn't answer my question ?
The reason I asked those earlier is because it would give us more of an indication of the rest of the install.

 

[IAmSparkytus!]

I don't think anyone is trying to belittle you Mate, it just seems odd that with your quals and experience you are asking questions that you should be aware of.

Thanks, Pete999. I may have took his comment in the wrong context so I apologise.

Like I said, I’m asking because it didn’t seem right to myself but the NIC assessor told me he didn’t see a problem with it, and his reply to my question when I asked him offered nowhere near as much feedback as what you guys have offered and that is all I was looking for which I appreciate.

 

[IAmSparkytus!]

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 ?

Sorry, AJshep, I missed this.

Twin and earths from a distribution board fed from individual C curve MCBs, ranging from 6A to 20A I believe if I remember correctly, terminated into rotary isolators adjacent to the motor units with a twin and earth tail from the isolators into the motor connections.

 

[AJshep]

Sorry, AJshep, I missed this.

Twin and earths from a distribution board fed from individual C curve MCBs, ranging from 6A to 20A I believe if I remember correctly, terminated into rotary isolators adjacent to the motor units with a twin and earth tail from the isolators into the motor connections.

So no DOL or any form of overload protection for the motors either..
Id take a stab in the dark and say they are bigger than 370w.
Sounds like the person who installed it should have asked for advice or consulted the BS7671 first

Nobody knows everything, that's why we have the BS7671 for reference. Better to ask advice and get it right mate, so don't feel bad about asking for advice.
I think the guys on here are saying, sometimes it's down to you to make a Professional judgement. The information the NICEIC gave you about using T&E was probably right, but it would depend on various other factors, that you/we as skilled professionals would notice while we were on site.

From everything you described it doesn't comply.

 

[westward10]

What do you think ToonSparky about the way it is done. You have our opinions but what is yours.

 

[IAmSparkytus!]

What do you think ToonSparky about the way it is done. You have our opinions but what is yours.

I personally wouldn’t have chosen to install the circuits the way they have been but that doesn’t mean to say the job has been done incorrectly.

 

[Pete999]

1

I personally wouldn’t have chosen to install the circuits the way they have been but that doesn’t mean to say the job has been done incorrectly.

You still haven't answered the question"how d you intend to enter the isolator using twin and cpc?"

 

[ipf]

I personally wouldn’t have chosen to install the circuits the way they have been but that doesn’t mean to say the job has been done incorrectly.

It just goes to show that just completing a job that complies with regulations isn't necessarily the correct way to go about it. The advice gained from NICEIC regarding compliance is from someone who knows as much about the installation as we do. From the info given, it doesn't sound good to me, but the one in the best position is yourself.

 

[ipf]

1
You still haven't answered the question"how d you intend to enter the isolator using twin and cpc?"

It's been done already, hasn't it, Pete?