# Cable size

Discuss Cable size in the Commercial Electrical Advice area at ElectriciansForums.net

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#### alberto

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I am going to buy a generator 92 kVA, and I need to know what size of cable I have to choose. My consumption is 90 kVA.

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#### malcolmsanford

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Arms

Ask away to the all seeing and all knowing omnipresent one ........................or

You can give a bit more information like length of runs, type of cable, type of environment, cabled buried or not

#### telectrix

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Arms
Esteemed
at 230v 90KVA equates to just under 400A, so check your cable ratings, allowing for installation method. but if' it's 3 phase, then a different situation.

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#### Guest123

Nowhere near enough info there OP, I can only assume we are looking at 3P here???

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#### alberto

It is 3ph generator, 40m length of cable.

K

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#### Guest123

Sizing a genny is often where a lot of guys come unstuck.

Gennys dont like being under OR overloaded, you need to consider voltage dip, frequency dip, duty cycle. peak loading, resistive/inductive loads, phase balancing etc etc.

My rule of thumb is >30% continuous rating and <80% continuous rating.

IMO you need to start looking at a 110KVA minimum and then factor in the variables.

90KVA

A

#### alberto

Thanks a lot Lenny. I already have taken into consideration power factor. I have chosen 114kVA which it gives 92kVA. All what I need to know is: What size of cable do I have to use? According to my calculation I'm going to use 70mm2 which is enough for my consumption.
Thanks again

A

#### aprillove1719

The installation is supplied through a 630 kVA transformer. ... a high degree of supply continuity and part of the installation can be supplied by a 250 kVA standby generator. ... Length (m), 5, Cable voltage drop ΔU (%), 0.53

K

Where did you get that info?

E

#### Engineer54

Sizing a genny is often where a lot of guys come unstuck.

Gennys dont like being under OR overloaded, you need to consider voltage dip, frequency dip, duty cycle. peak loading, resistive/inductive loads, phase balancing etc etc.

My rule of thumb is >30% continuous rating and <80% continuous rating
.

IMO you need to start looking at a 110KVA minimum and then factor in the variables.

90KVA
A decent manufactured Genny engine and alternator will happily run at it's continuous rating for the manufacturers specified times. It'll also generally have the capacity to run for certain periods at 110% of it's continuous rating. What they definitely don't like, is being run underloaded. I wouldn't run a stand-by or prime power Genny at under 60 to 70%, especially if it's a 2 stroke engine, which make for the best stand-by Genny set-ups.

But having read you post again, i think your talking more about initial sizing of the required Genny. In which case, you need to be pretty accurate on your ''actual load'' requirements, in order to accommodate any future load provision!!

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E

#### Engineer54

The installation is supplied through a 630 kVA transformer. ... a high degree of supply continuity and part of the installation can be supplied by a 250 kVA standby generator. ... Length (m), 5, Cable voltage drop ΔU (%), 0.53

Your basically just describing an installations Switchboard/MDB, that has a essential and non-essential facility...

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#### Guest123

But having read you post again, i think your talking more about initial sizing of the required Genny. In which case, you need to be pretty accurate on your ''actual load'' requirements, in order to accommodate any future load provision!!
I was, this is what I was trying to get the OP to give us, type of loading, duty cycle, etc etc etc.

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#### Engineer54

I was, this is what I was trying to get the OP to give us, type of loading, duty cycle, etc etc etc.
I must slow down my speed reading, or at least read a post 2 or 3 times!!! ...lol!!!

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