Three phase DB, water, you can geuss!

[Engineer54]

Now explain to me why there is nothing wrong with it? I dont quite see it?

If you have 2x cables capable of 30a each, running a 50 a load, and one leg fails, you end up with one cable running 50a thats only rated to 30a?

I think you would have to explain to me why would one leg fail?? Running ''Parallel'' supplies is standard practice, it can increase current carrying abilities, reduce volt drop, reduce labour costs and in many circumstances, reduce the overall cost of the installation over using a far larger sized single cable!!

Most of the supplies feeding our main switch boards and most sub switchboards on this and every other project i've ever worked on, will use parallel supplies, and i'm not talking of just 2 parallel cables but several per phase & N etc!!! Your talking about a couple of cables supplying 50A, and i'm talking of several cables supplying 3500A!!! Now think about the size of a single cable supplying that sort of load, ...doesn't bare thinking about does it?? ...lol!!!!

Standard Practice as i stated before!!!

 

[J25GTi]

I think you would have to explain to me why would one leg fail?? Running ''Parallel'' supplies is standard practice, it can increase current carrying abilities, reduce volt drop, reduce labour costs and in many circumstances, reduce the overall cost of the installation over using a far larger sized single cable!!

Most of the supplies feeding our main switch boards and most sub switchboards on this and every other project i've ever worked on, will use parallel supplies, and i'm not talking of just 2 parallel cables but several per phase & N etc!!! Your talking about a couple of cables supplying 50A, and i'm talking of several cables supplying 3500A!!! Now think about the size of a single cable supplying that sort of load, ...doesn't bare thinking about does it?? ...lol!!!!

Standard Practice as i stated before!!!

Well having never seen it done before I wouldn't know! Seems a bit odd that you can do it. Because I was always taught not to ask why would a leg fail, but to ask what happens when it does fail?

Surely a an mcb etc has to be rated to the lowest conductor carrying capacity. Of which this conductor would be 30amps?

 

[Smudge]

I think you would have to explain to me why would one leg fail?? Running ''Parallel'' supplies is standard practice, it can increase current carrying abilities, reduce volt drop, reduce labour costs and in many circumstances, reduce the overall cost of the installation over using a far larger sized single cable!!

Most of the supplies feeding our main switch boards and most sub switchboards on this and every other project i've ever worked on, will use parallel supplies, and i'm not talking of just 2 parallel cables but several per phase & N etc!!! Your talking about a couple of cables supplying 50A, and i'm talking of several cables supplying 3500A!!! Now think about the size of a single cable supplying that sort of load, ...doesn't bare thinking about does it?? ...lol!!!!

Standard Practice as i stated before!!!

common practice at my place of work to run parallel supplies, easier when working with larger swa's etc. Welcome by the way, neat install too.

 

[spark 68]

I have to agree with E54 on this, it is industry standard practice to use parallel feeds, especially with the larger cables sizes for the reasons he has given, ie. practicality and costs.

 

[Engineer54]

Well having never seen it done before I wouldn't know! Seems a bit odd that you can do it. Because I was always taught not to ask why would a leg fail, but to ask what happens when it does fail?

Surely a an mcb etc has to be rated to the lowest conductor carrying capacity. Of which this conductor would be 30amps?

That, would frankly defeat the point wouldn't it?? Most main switchboards, will actually be constructed to accommodate parallel feeds and in some circumstances even outgoing ways...

Not sure why you are obsessed with one leg failing, why would just one leg fail? Taking that all connections have been professionally made off, what would you say, is the chances of that ever happening??

 

[Engineer54]

It should be pointed out that there ARE certain rules that govern the use of parallel supplies/feeds. The cables Must be of the same construction, Must be of the same CSA size, Must be substantially the same length point to point, should follow the same route in/by the same containment means.

Remember, we are not talking about a ring circuit, although a ring can be classed as a crude parallel circuit but one that serves multiple loads/points. However a true parallel circuit will supply/feed just one load point!!

 

[J25GTi]

That, would frankly defeat the point wouldn't it?? Most main switchboards, will actually be constructed to accommodate parallel feeds and in some circumstances even outgoing ways...

Not sure why you are obsessed with one leg failing, why would just one leg fail? Taking that all connections have been professionally made off, what would you say, is the chances of that ever happening??

I'm not obsessed with it. Just asking the wquestions that's all, as obviously there is something I have missed here!

 

[Engineer54]

I'm not obsessed with it. Just asking the questions that's all, as obviously there is something I have missed here!

Probably something else that's not covered in an electricians training these days... :sick: lol!!!

 

[Knobhead]

As an industrial electrician you must have come across a service head like this. A Lucy 630A unit (spreader boxes not shown).
View attachment 12183
If you can’t run parallel cables, why are there 2 cable outlets per phase.
As has been said in industry parallel cables are normal practice.

 

[J25GTi]

As an industrial electrician you must have come across a service head like this. A Lucy 630A unit (spreader boxes not shown).
View attachment 12183
If you can’t run parallel cables, why are there 2 cable outlets per phase.
As has been said in industry parallel cables are normal practice.

Yes of course I have seen these, but I've never used parrallel supplies etc. Only single cables up to 5 core 195mm. But we live and learn

 

[Knobhead]

Given the choice would you prefer to run a 185 or two 95’s. I know which my moneys on.

 

[Engineer54]

Yes of course I have seen these, but I've never used parallel supplies etc. Only single cables up to 5 core 195mm. But we live and learn

Are you convinced yet, that there is nothing wrong with a parallel circuit run?? And, ...can you now see the benefits that such circuits can bring to an installation, in both current carrying etc and cost savings in labour and cable costs??.... These can be very significant in larger projects, especially where long cable runs are involved...

 

[Brightspark2]

Good work, massive improvement there...


Once you start getting to larger CSA's, cables ran in parallel get more common for reasons already stated. Im just completing an installation in a data centre where we have run various cables in parallel, 2 x 185mm etc.

 

[Mark_Burgess]

Lets hope they have sorted the leak in the roof!!
What I would say is, it looks if the MCB they put in is the right way round, the MCB spring clip is supposed to be on the outside, well hager boards always state it.

 

[RISElectrical]

Cables ran in Parallel as stated are fine. If we worked on the principal of "when" a leg fails, a 2.5mm ring would either need to be on a 20A MCB or wired in 4mm as what your saying contradicts the design of a ring final circuit