Parallel Supplies

[Silly Sausage]

hoo hoo Can I join in this thread?? I'll invite Eng54 as well...

Hahaha!! We remember the previous thread well!
Find the link to it...

 

[Knobhead]

Zzzzzzzzzzzzzz

I wish!

 

[Spoon]

Hahaha!! We remember the previous thread well!
Find the link to it...

Just for you and Tony
http://www.electriciansforums.co.uk...-under-buildings-backed-up-200-amp-fuses.html
There are only 143 posts to read...

 

[Knobhead]

One of my first jobs when let loose on the plants as an apprentice was running 10 parallel and 2 triple feeds. All 185mm² PILCSWA.

I’ve been using parallel feeds ever since they make sense to me. The cable gangs didn’t complain either.

 

[Silly Sausage]

Cheers Spoon, one of my favourite threads...funny!

 

[Spoon]

Cheers Spoon, one of my favourite threads...funny!

It was a bit frustrating for me as no one was giving me an answer to my question. It was only until post 129 that things became more clear.
I would like to thank Eng54 for bearing with me on that thread and also Rockingit. (Also everyone else who helped me)
I always want to learn new things but being an engineer I need to know why things work as they do and sometimes this needs to be explained to me in layman's terms...

 

[Engineer54]

It was a bit frustrating for me as no one was giving me an answer to my question. It was only until post 129 that things became more clear.
I would like to thank Eng54 for bearing with me on that thread and also Rockingit. (Also everyone else who helped me)
I always want to learn new things but being an engineer I need to know why things work as they do and sometimes this needs to be explained to me in layman's terms...

Ah, the saga of applying a grouping factor to a single circuit, i remember that farce well!! lol!!

 

[Guest55]

Ah, the saga of applying a grouping factor to a single circuit, i remember that farce well!! lol!!

good debate though.
and i agree with your assessment of applying grouping only to seperate circuits not multi-feeds of 1 supply

 

[Spoon]

good debate though.
and i agree with your assessment of applying grouping only to seperate circuits not multi-feeds of 1 supply

so do I, now...

 

[Darkwood]

Digressing back to the OP query and against the general opinion of the responses.... yes you can have parallel cable runs of differing size cables of the same supply but certain measures and extra protection is required but with regards to the OP trying to save a penny or too and for the majority of these set-ups then no you wouldn't have variable size cables withing the same parallel system.

 

[Knobhead]

I know it’s a rotten question.

DW would you run an unequal parallel feed?
I wouldn’t. But economics claws its way in to everything.




Until later in my working life accountants didn’t enter the equation. Tony wants, Tony gets.

I went in to engineering planning and procurement. Tony wants, Tony can get stuffed! It’s not coming out of this month’s budget!


BTW if anyone thinks of going in to procurement DON’T. You’re the whipping boy for both sides!

 

[Darkwood]

With the nature of my jobs Tony i very much doubt id be ever in a position of needing to consider wiring unequal parallel cabling/loading but if it did ever crop up i find absolutely no issue with it as long as loading on each core is monitored respective to its rating..... but if your in a position to be asking the questions regarding whether its allowed or not then saying no is often the simplest answer as Appendix-10 and even 11 will highlight to the OP with the calculations and considerations required to ensure a safe set-up.

 

[Engineer54]

With the nature of my jobs Tony i very much doubt id be ever in a position of needing to consider wiring unequal parallel cabling/loading but if it did ever crop up i find absolutely no issue with it as long as loading on each core is monitored respective to its rating..... but if your in a position to be asking the questions regarding whether its allowed or not then saying no is often the simplest answer as Appendix-10 and even 11 will highlight to the OP with the calculations and considerations required to ensure a safe set-up.

I can't think of any situation, where i would be happy to allow parallel cabling of differing sizes, unequal lengths, and/or of differing cable construction. God only knows what would happen in the future as additional loads etc, creep into the equation.... As far as i'm concerned it's an absolute No, No!!

 

[Darkwood]

I can't think of any situation, where i would be happy to allow parallel cabling of differing sizes, unequal lengths, and/or of differing cable construction. God only knows what would happen in the future as additional loads etc, creep into the equation.... As far as i'm concerned it's an absolute No, No!!

As a rule im in agreement it was just to explain it isn't in fact against regulation just comes with a lot of calculation and protective arrangements to be considered.

Any parallel cabling system is fundamentally at a disadvantage regarding overload protection of the separate cores as a number of issues can arise to create unequal loading but namely faults, i would never implement an unequal loaded system into any design without it been a last resort and all other options gone whether it arises from variable size cores or differing paths/lengths ....in a nutshell i probably never will but its to be noted it is an acceptable method when done correctly.

CT monitoring of each core with full linked 3ph tripping is one way to go, this give a higher degree of protection than the standard equal size/run parallel system would have so in reality it might not be the normally chosen method but is in fact better protected, they are other way to protect unequal loaded systems that IMHO fall short of my comfort zone but they still are acceptable within the BS7671 and BS7769 will give guidance in correct calculations.

Again i'm not promoting the system or trying to nudge the OP he might be able to use such a set-up just that the general response to say its a big NO NO! isn't true its just 99% of us would never entertain employing the use of such a method but it shouldn't be said that it should never be done.

 

[Engineer54]

As a rule im in agreement it was just to explain it isn't in fact against regulation just comes with a lot of calculation and protective arrangements to be considered.

Any parallel cabling system is fundamentally at a disadvantage regarding overload protection of the separate cores as a number of issues can arise to create unequal loading but namely faults, i would never implement an unequal loaded system into any design without it been a last resort and all other options gone whether it arises from variable size cores or differing paths/lengths ....in a nutshell i probably never will but its to be noted it is an acceptable method when done correctly.

CT monitoring of each core with full linked 3ph tripping is one way to go, this give a higher degree of protection than the standard equal size/run parallel system would have so in reality it might not be the normally chosen method but is in fact better protected, they are other way to protect unequal loaded systems that IMHO fall short of my comfort zone but they still are acceptable within the BS7671 and BS7769 will give guidance in correct calculations.
Again i'm not promoting the system or trying to nudge the OP he might be able to use such a set-up just that the general response to say its a big NO NO! isn't true its just 99% of us would never entertain employing the use of such a method but it shouldn't be said that it should never be done.

Come on now, CT protection monitoring of each core of a parallel circuit?? Now who in their right mind would ever employ such a method to get over two or more unequal parallel cable sizes!!!! Apart from anything else, it'll be a very expensive fix, and probably beyond the capabilities of many modern day electricians, outside of the industrial sector. There are unconventional ways around many things, but would anyone really go to those sort of lengths, ...i don't think so!!

The use of differing cable sizes in a parallel circuit is for all intent and purposes, is and has always been a complete No, No!!