Parallel Supplies

Discuss Parallel Supplies in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Is there amything wrong with having a parallel supply, that will consist of 2 different size cables?

for examples say cable 1 = 25mm, cable 2 = 10mm.

To give a 35mm
 
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If you're on a Naval ship, at war in the middle of the sea and having to make do with whats available right now, then yes.

What is the context Mr Enigma?
 
I can't think of a regulation to quote you why its a bad idea, just feels bad.

For instance if you have two runs supplying the ... Supplied thing, and at a
later date one cable of the two is damaged / disconnected ..... Well then the other one may become overloaded without anyone noticing
 
that could happen even if both cables were equal size.

if he insists on parallel conductors, at least run in another 25mm. then you'll have some extra capacity for future increase in loading.
 
My BGB is in the car but from memory I thought the cables would have to follow the same route and be the same CSA.....but I may well be wrong.
 
was thinking to use same size, and of course they will follow the same route, which wiould be in a duct in the ground. So good protection.
 
twin / parallel feeds are pretty common on submains larger than 300mm.

struggling to think of anything else to add to be honest lol.

er , carry on.

;-)
 
hoo hoo Can I join in this thread?? I'll invite Eng54 as well... :)
 
Parallel circuit/supply needs all conductors to be of the same CSA, follow the same route, cables be of the same type and construction. Parallel circuits can consist of several conductors/cables not just two. Such circuits can and do offer many advantages over a single much larger conductor/cable installation....

If designing the OP's circuit from scratch probably 2 X 16mm would be selected, but in some circumstances even 2 x 10mm could replace a single 35mm cable....
 
so, in a nutcase, sorry, nutshell, as OP already has a single 25mm, the solution is to parallel a second 25mm cable in.
 
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.
 
Archy Styrigg said:
Cheers Spoon, one of my favourite threads...funny! :)
Click to expand...

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...
 
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Spoon said:
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...
Click to expand...

Ah, the saga of applying a grouping factor to a single circuit, i remember that farce well!! lol!!
 
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.
 
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!
 
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.
 
darkwood said:
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.
Click to expand...

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!!
 
Engineer54 said:
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!!
Click to expand...
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.
 
darkwood said:
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.
Click to expand...



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!!
 
Yes probably overkill E54 but it would do the job and on a large scale upgrade of existing could actually be the most cost effective method but as i said i was just throwing it out there that it isn't against reg's if calculated correctly - but agree beyond your average Electrician out there so yes following the rule of thumb always same csa, length and route.
 
darkwood said:
Yes probably overkill E54 but it would do the job and on a large scale upgrade of existing could actually be the most cost effective method but as i said i was just throwing it out there that it isn't against reg's if calculated correctly - but agree beyond your average Electrician out there so yes following the rule of thumb always same csa, length and route.
Click to expand...

Why would anyone, least of all a Design Engineer leave a parallel circuit in place with differing CSA on a large scale upgrade, that would be defeating the whole point of the upgrade.

I know what you're saying, but as i said earlier there are always way's to get over an existing problem, but 9 X out of 10 the additional costs and hassle just aren't worth not doing the job properly... lol!!
If the reg's condone such an installation, i haven't come across it. I'll have to have a look later today, if i have time.
 
Engineer54 said:
Why would anyone, least of all a Design Engineer leave a parallel circuit in place with differing CSA on a large scale upgrade, that would be defeating the whole point of the upgrade.

I know what you're saying, but as i said earlier there are always way's to get over an existing problem, but 9 X out of 10 the additional costs and hassle just aren't worth not doing the job properly... lol!!
If the reg's condone such an installation, i haven't come across it. I'll have to have a look later today, if i have time.
Click to expand...

I agree and see why your reaction to my original comment now, im jumping between forums and was on auto pilot the variable sized cores comment was relative to single cores in parallel across phases; if i remember rightly you are required to maintain equal csa on the same phase but can in certain set-ups have other phases of different csa (although not as a standard install of a 3ph supply with linked O/L protection across the phases). I didn't mean variable sizes between the same phase.... relative to 2 or more multicore cables in parallel then this doesn't apply to that senerio as yes equal csa required deffo....

It was merely an extreme example to back up my suggestion that parallel systems do function correctly and safely with unequal load sharing if designed carefully and protected properly.

This i got carried away here and went on a non-constructive tangent but ill see if i can reference what i mean another time as its time for the pit. :)
 
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Can we stop the squabbling.

Equal parallel feeds = Good
Unequal parallel feeds = Not good, but with proviso’s acceptable.

I ran a 240mm² PVCSWA to bolster two 0.3 PILCSWA’s. Not ideal but it got our arse out of the fire. The PILCSWA terminations had been done with wax (only time I’ve ever seen this). They were so hot they were spitting wax out of the termination.

Needs must at times!

The switchgear catching fire is another story :smilielol5:
 
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