Cable Sizing For Large Motor

Advertise with us
Shop deals on ebay
armeg
shop deals on amazon
Talk Electrician Forum

Help Support Talk Electrician Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
B

BASIB

Guest
Hi All

Need a bit of help here as in what cable to use and price for - My first thoughts are SWA but I'm not sure

I have been asked to wire up an AC motor to a Variable Speed Drive

The run is 7 meters long 

The motor draws 713 amps full load current and they have told me the installed cable has to comply with EMC requirements

The Variable speed drive is an Schneider Brand and has 10% overload capability

All thoughts would be greatly appreciated

Thanks

Jimmy

I forgot to say - this is a little larger than the normal jobs i do so could do with some help

Thanks

Jimmy

 
Last edited:
No idea,

Way beyond me, unless I'm beered, then I'll tell you rubbish,

But, we have a few good ind and motor sparks on here who I'm sure will be about soon.

 
EMC bit is easy - swa and earthed armouring sorts that out.

Bit more info would be good ie 713Amps, per phase or total? Did you look at what's currently fitted as a guide to what area you should be in?

 
713 Amps !!!!!!!     Is there a decimal point in there somewhere?      You'd have to warn  the National Grid before you started that ****** up .   ( Its not watts is it ?)

It didn't come with a 13A plug on it then  ?  :innocent

 
Last edited by a moderator:
binky said:
EMC bit is easy - swa and earthed armouring sorts that out.

Bit more info would be good ie 713Amps, per phase or total? Did you look at what's currently fitted as a guide to what area you should be in?
Click to expand...
Not quite, SWA does not normally comply with the EMC requirements for VSD's

BASIB said:
Hi All

Need a bit of help here as in what cable to use and price for - My first thoughts are SWA but I'm not sure

I have been asked to wire up an AC motor to a Variable Speed Drive

The run is 7 meters long 

The motor draws 713 amps full load current and they have told me the installed cable has to comply with EMC requirements

The Variable speed drive is an Schneider Brand and has 10% overload capability

All thoughts would be greatly appreciated

Thanks

Jimmy

I forgot to say - this is a little larger than the normal jobs i do so could do with some help

Thanks

Jimmy
Click to expand...
Welcome to the forum.

This is outside the remit of BS7671 really.

With the info in your OP, this is really inadequate to provide a definitive answer.

For a drive of this size, IF it is circa 700A per phase then it must be correctly designed.

Are you being asked to do the design also?

If not just connect it as per the design you are given.

 
Its 713 amps per phase

The motor is 400Kw at 400 Volts Delta

The inverter is a schneider

The customer has bought the inverter and motor from schneider and wants it installed and cabled, schneider sales man just did a supply only as they don't do install or design

 
sprocketflup said:
Are you sure you're up to this job? I mean, if its done incorrectly the consequences don't bear thinking about
Click to expand...

whats the worst that could happen?!

then again its probably the water pump for the building fire sprinkler system, and you dont want that to fail when the motor is on fire because someone wired it in the wrong flex

 
I think BASIB is winding us up to be honest .

His profile is :-  Domestic , unskilled , Short course , DIYer .    So just the bloke you'd ask to design & install  a 400 kw  700A  per phase motor .  :innocent

 
Last edited by a moderator:
Spookily I have just done 2 x 399 kW refrigeration compressors on Danfoss VSD's backed up by 800amp MCCB's. These are cabled with 300 mm awa singles with a 150 mm overlay.

 
Also I'm assuming that the customer has a large enough supply coming in to handle the load

Canoeboy said:
Depends on what the compressor specs are but 300sq.mm awa seems a bit small for 399kW

Unless they are freezer duty with suction regulators, i digress though......

And i absolutely hate SWA and AWA - there are so many much more nicer cables out there - perhaps i am just getting too old - or grumpy - or grey.......
Click to expand...
This was the size specified by the designer. I also don't like using SWA and similar as trying to gland and connect them into the inverters is a nightmare.

Unfortunately nobody does a screened cable of this size other than armoured.

 
By the time you take into account PF and efficiency, i would have thought more like 400Hp... Still, that is one hell of a motor... Does sound like a wind up to me though. Nobody in their right mind would just ring up an electrical firm and say; "Hello? Yes, hmm, i'd like to buy a motor please, do you have any around, hmm, say, 400hp?? Oh, and I'd like a VFD to go with it"

What would that sort of kit cost??? Nearly as much as the substation and your own pylon you would need to power it!!!

john...

 
Canoeboy said:
I did a job 3 years ago now on a military inverter test rig - cable was 3 x 900 sq mm singes EMC Screened - flexible like a bit of 25sq mm tails 

Its available ex stock in Germany and complies to all worldwide standards and they do 360 degree EMC glands for it as well

Trouble with some designers is they don't live in the real world and are archaic in that they do not know what is available 

The other thing is if they HAD ever had to put in a 300sq.mm cable into a motor or inverter then they would NEVER specify it again

And as per SW's post - Armoured may not comply with EMC

All the EMC cables i have used for EMC compliance are CY - Copper Braid not Steel Braid.......
Click to expand...
Would you have the company name by any chance as we and all our cable suppliers could not source anything like what you have mentioned, be handy for future reference cheers

 
Send me a PM with your gmail address and I'll send you a guide. It's a 4.5 Meg PDF so I can't attach it here I'm afraid.

*edit* I split the pdf and extracted just the relevant EMC section but it still weighs in at 1.6Mb and I still can't attach it so it's definitely need to be emailed..

 
Last edited by a moderator:

Similar threads

Pwablo
RFI From Inverter
2 3 4
Replies
75
Views
4K
UNG
U
M
BOAT YACHT HVAC - Unbalanced Phases and Harmonics - Single-phase motor coggs only when feed from generators.
Replies
2
Views
627
Miami Boat Electrician
M
B
My new system has now been commissioned
Replies
6
Views
812
Bob Smith
B
J
Cable Sizing Query/Confirmation
Replies
2
Views
995
Phoenix
P
C
Advice needed scoping work for electrician
2
Replies
23
Views
2K
apprentice87
apprentice87

Latest posts

Top