double up on swa submain

[pete555]

recently had a test with 2 cables being used for sub main

1st is a 10mm swa 2 core with armourings for earth

2nd is a 6mm swa 3 core with armour and integral earth

both cables doubled up on MCCB 63 a breaker
and both terminated in DB

what code

i think 2

ive told them its grim and needs 1 cable to go but not sure if i should have coded it a 1

 

[yellowvanman]

What reg is applicable?

Not saying its right or wrong but you may need to read Appendix 10

 

[Silly Sausage]

I take it you mean they're in parallel?
If so, it'll contravene the parallel cables reg.
E54's your man for this one.

 

[Knobhead]

All I'll say is one of the cables has to go.

I’ve run many parallel feeds, it’s easier. Both cables of the same length and construction.

 

[Engineer54]

recently had a test with 2 cables being used for sub main

1st is a 10mm swa 2 core with armourings for earth

2nd is a 6mm swa 3 core with armour and integral earth

both cables doubled up on MCCB 63 a breaker
and both terminated in DB

what code

i think 2

ive told them its grim and needs 1 cable to go but not sure if i should have coded it a 1

There is absolutely nothing wrong with parallel supply cabling, in fact they can give many advantages over the use of a single larger cable. So if correctly installed, it's certainly not Grim!!!

This set-up however, contravenes at least two of the parallel cable rules, one being that both cables must be of the same CSA, and the other, must be of the same construction!! Also they should physically follow the same route (same length)...

 

[loop3]

54, you know your ****. Cables in parallel must be of the same length construction and cross sectional area. And to ensure some of the above - run the same path. And just to reiterate for swa. You can use the armour as the cpc as long as you calculate it to be worthy!

 

[yellowvanman]

There is absolutely nothing wrong with parallel supply cabling, in fact they can give many advantages over the use of a single larger cable. So if correctly installed, it's certainly not Grim!!!

This set-up however, contravenes at least two of the parallel cable rules, one being that both cables must be of the same CSA, and the other, must be of the same construction!! Also they should physically follow the same route (same length)...

Not wanting to disagree as I've not done this myself but in Appendix 10 (BRB - maybe a different appendix number in BGB) does say:

"Where the difference in impedance between parallel conductors causes unequal current sharing, for example greater than 10% difference, the design current and requirements for overload protection each conductor should be considered individually"

The maths for this looks a bit complicated but its certainly not saying its prohibited. In practise because of the maths it maybe a bit more difficult, but if a 'serious' observation (potential high cost to rectify) is going to be made on a EICR then the author may need to back up his recommendation.

 

[Silly Sausage]

Eeeee...I like a challenge!
It's an area I'm not, and ever likely to be, involved in, but stuck inside tonight with kids (she's off on the razz)...

 

[Engineer54]

Not wanting to disagree as I've not done this myself but in Appendix 10 (BRB - maybe a different appendix number in BGB) does say:

"Where the difference in impedance between parallel conductors causes unequal current sharing, for example greater than 10% difference, the design current and requirements for overload protection each conductor should be considered individually"

The maths for this looks a bit complicated but its certainly not saying its prohibited. In practise because of the maths it maybe a bit more difficult, but if a 'serious' observation (potential high cost to rectify) is going to be made on a EICR then the author may need to back up his recommendation.

Why do you think the rules for installing parallel cables stipulate all cables MUST be of the same CSA, MUST be of the same overall LENGTH, and MUST be of the same construction. Complying with these conditions, will totally negate the above paragraph you posted!! It's ''Standard Practice'' in both industrial and larger commercial installations...

I would guess that over 90% of all the main distribution supplies on this project is by multiple Parallel cabling (not just 2 cables in parallel). I would like your suggestion how you would supply, say a 3200A main switchboard from a distribution transformer using single core cables, or if you like SWA cables?? ...lol!!

 

[Darkwood]

I run parallel cable sets all the time and as already pointed out its a great way to cut costs and make install easier but as for comments i think all that needs to be said has already been...

 

[Engineer54]

54, you know your ****. Cables in parallel must be of the same length construction and cross sectional area. And to ensure some of the above - run the same path. And just to reiterate for swa. You can use the armour as the cpc as long as you calculate it to be worthy!

Most of the larger SWA cables, steel wire CSA will not meet those requirements.

One of the biggest advantages of running a parallel supply is that you can use much smaller CSA cables to supply loads that would require a relatively much bigger cable if being supplied with a single cable.

 

[i=p/u]

so 5x10mm or 1x50mm...... comon

 

[yellowvanman]

Why do you think the rules for installing parallel cables stipulate all cables MUST be of the same CSA, MUST be of the same overall LENGTH, and MUST be of the same construction. Complying with these conditions, will totally negate the above paragraph you posted!! It's ''Standard Practice'' in both industrial and larger commercial installations...

Where are those rules as they are not in BS7671 as far as I'm aware? I agree its good practise to make sure all things are equal, but in this case they are not and the BGB basically says thats Ok with special consideration! Hence the guy doing the EICR needs to be sure of his facts if he is going to recommend additional work.

I would guess that over 90% of all the main distribution supplies on this project is by multiple Parallel cabling (not just 2 cables in parallel). I would like your suggestion how you would supply, say a 3200A main switchboard from a distribution transformer using single core cables, or if you like SWA cables?? ...lol!!

What's that got to do with this thread?

 

[Engineer54]

Where are those rules as they are not in BS7671 as far as I'm aware? I agree its good practise to make sure all things are equal, but in this case they are not and the BGB basically says thats Ok with special consideration! Hence the guy doing the EICR needs to be sure of his facts if he is going to recommend additional work.




What's that got to do with this thread?

You obviously totally rely on BS7671 for all the answers, and if it's not in there, then something has just got to be wrong!! lol!! Well i have some devastating news for you, BS 7671 (and it's OSG's) is/are only a guide it is not and never has been the definitive bible you seem to think it is. Broadly speaking it's scope is also somewhat limited and would be almost impossible to cover everything. It also assumes, that the reader has a broad understanding of electrical technology.

Wrong the guy undertaking an ECIR needs to be experienced, knowledgeable and competent enough to be able to conduct and assess the installation he is inspecting/testing and be capable of advising on any remedial work that may be necessary, without having to always confer with a guide book of Reg's!!

What has my last paragraph got to do with this thread?? Well if you think about it for a second or two, ...what single cable size would be capable of supplying 3200A?? NONE, this is/was a perfect example to show you that parallel cabling is the only way that it would be possible to interconnect between the source and the main switchboard... Yes there are other methods, but we are talking about cabling solutions...

 

[Simlec]

Where are those rules as they are not in BS7671 as far as I'm aware? I agree its good practise to make sure all things are equal, but in this case they are not and the BGB basically says thats Ok with special consideration! Hence the guy doing the EICR needs to be sure of his facts if he is going to recommend additional work.

Is that not 523.7 -(i)

 

[yellowvanman]

Where are those rules as they are not in BS7671 as far as I'm aware? I agree its good practise to make sure all things are equal, but in this case they are not and the BGB basically says thats Ok with special consideration! Hence the guy doing the EICR needs to be sure of his facts if he is going to recommend additional work.

Is that not 523.7 -(i)

OK, but (ii) seems to give a get out. As I've stated before if I was doing something similar I wouldn't contemplate different sized cables.

 

[Engineer54]

so 5x10mm or 1x50mm...... comon

Wrong!! lol!!

 

[Engineer54]

OK, but (ii) seems to give a get out. As I've stated before if I was doing something similar I wouldn't contemplate different sized cables.

There is no get out!! Parallel circuits are standard everyday practice, end of!!

The parallel installation in the OP's case is wrong, it contravenes parallel circuit criteria in at least 2 instances that we know about. So you were right to pick this up and code it...

 

[yellowvanman]

You obviously totally rely on BS7671 for all the answers, and if it's not in there, then something has just got to be wrong!! lol!! Well i have some devastating news for you, BS 7671 (and it's OSG's) is/are only a guide it is not and never has been the definitive bible you seem to think it is. Broadly speaking it's scope is also somewhat limited and would be almost impossible to cover everything.

I work to BS7671 because thats relevant to what I do and to what most people do on the forum and for the Op this is probably the most relevant document for his situation, he can correct me if I'm wrong. On your project you may work to other documents thats fair enough but are they relevant to what I (and maybe the OP) do - unlikely?

It also assumes, that the reader has a broad understanding of electrical technology.

Are you trying to imply I don't?

Wrong the guy undertaking an ECIR needs to be experienced, knowledgeable and competent enough to be able to conduct and assess the installation he is inspecting/testing and be capable of advising on any remedial work that may be necessary, without having to always confer with a guide book of Reg's!!

There are very few people who don't have to refer to the regs at sometime. The whole point of an EICR is to make observations and back that up with a reason which is usually associated with a reg no. No-one would be able to quote every reg number and sometimes you see something it maybe doesn't look right but when you delve deeper you find it maybe ok or the actual reason why it doesn't look right. In the case of the OP, he's seen something that doesn't look right, I'm just pointing to something that MAY show it is OK. What he choses to do with that information is up to him, he's the one signing the EICR.

What has my last paragraph got to do with this thread?? Well if you think about it for a second or two, ...what single cable size would be capable of supplying 3200A?? NONE, this is/was a perfect example to show you that parallel cabling is the only way that it would be possible to interconnect between the source and the main switchboard... Yes there are other methods, but we are talking about cabling solutions...

But the thread has got nothing to do with this. I've already agreed that I wouldn't use different cables so what are you trying to prove? We all know you are knowledgable but sometimes your arrogance and intolerance of others just winds me up!

 

[i=p/u]

back to original post never mind shag bagging each other, there is no right or wrong,,, they should be routed and sized the same..

 

[Engineer54]

I work to BS7671 because thats relevant to what I do and to what most people do on the forum and for the Op this is probably the most relevant document for his situation, he can correct me if I'm wrong. On your project you may work to other documents thats fair enough but are they relevant to what I (and maybe the OP) do - unlikely?

I work to various Country codes and regulations, including BS7671. Most overseas project specifications will denote ''designed and installed to the highest international standard''. And yes they are relevant as All those standards will say exactly the same thing as far as parallel circuitry is concerned!!

Are you trying to imply I don't?

I was pointing out that that your statement was misinformed... I have no idea if you, or come to that anyone else here have a broad understanding of electrical technology, i was merely making a statement...


There are very few people who don't have to refer to the regs at sometime. The whole point of an EICR is to make observations and back that up with a reason which is usually associated with a reg no. No-one would be able to quote every reg number and sometimes you see something it maybe doesn't look right but when you delve deeper you find it maybe ok or the actual reason why it doesn't look right. In the case of the OP, he's seen something that doesn't look right, I'm just pointing to something that MAY show it is OK. What he choses to do with that information is up to him, he's the one signing the EICR.

I'm not saying you shouldn't use the Reg's as a guide, just don't be surprised that what your looking for isn't covered, or doesn't give you a definitive answer. So finding a relative Reg number to substantiate a defect observation isn't always possible.


But the thread has got nothing to do with this. I've already agreed that I wouldn't use different cables so what are you trying to prove? We all know you are knowledgable but sometimes your arrogance and intolerance of others just winds me up!

Sorry i got a little confused as to who the OP was at this time. lol!! It was included to give an example of why parallel circuits are a standard everyday practice.

Sorry you feel that way, but i'm afraid you have to take me as you find me!! I certainly don't see myself in that light, and don't think that way either, but i suppose we all have our off day's.
I do know that my tolerance/patience levels are unfortunately not what they used to be!! ...lol!!!

 

[Engineer54]

back to original post never mind shag bagging each other, there is no right or wrong,,, they should be routed and sized the same..

So if they aren't, then it Must be Wrong, ...Right? ...LOL!!

 

[i=p/u]

could take 2 months too rewire due to nature of electrical installations right? as we dont know