Discuss Confirmation of SWA 3 Phase Cabe Size in the Commercial Electrical Advice area at ElectriciansForums.net

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M

matthewbutt

Hi All,

Firstly I hope this finds you all well. A quick question for an installation I need to order for tomorrow, I am not the electician but we are ordering the kit and I don't really fancy calling him on a bank holiday!

We are installing a large computer UPS which requires a 3 Phase 160A connection. The electrical intake room has more then enough capacity, thankfully, but just to double check that 50mm 4 Core SWA is the correct size for the job.

The cable run is ~33M, tied to cable tray, 30 degrees average temperature and I have included a 5% voltage drop. Would you calculations tie up with this?

Also I have been reading huge levels of debate on whether to use the armour as a CPC, purely out of interest is the safest method to run a seperate 25mm earth alongside the SWA as well as earth the armour? I feel I might be at risk of starting a debate here ;)

Thanks in advance for your time on this and I look forward to hearing back from you.
Kind regards,

Matthew
 
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Is the cable going through a caustic area which may attack the SWA?

If not I would install the 50mm without the extra CPC.

If the cable is on tray work in a benign environment why use SWA, why not go with a 5 core un-armoured cable?

Remember to look at the Rating Factors if there are other cables on the tray!

Is the cable 70 or 90 degrees Centigrade? 90 will help if the cable is with another cable on the tray!

Best still phone him up!!!!!!!!!!!!!!! to be sure
 
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Cheers for you help guys. I fully realise I could call him today, which I have now done, but it never hurts to learn from these topics!

In response to old_sparky_RE, no it is not a caustic environment and yes there is no need to use SWA except for we can't find a HO7 equivalent any cheaper and I thought it was the industry norm to run SWA for industrial applications and sub-metering etc. But noted, and taken onboard :).

In regards to the CPC, we will run one with it in additon - for the price of 30 metres of single core 25mm we may aswell protect ourselves completely. Better to be safe then sorry and all that!

On the topic of industrial electrics, we are having to sub-meter this 160A supply, would I be right in saying that CT's would be needed as standard loop-in/out boards aren't available with ratings this high? If so is their a 'normal' place to site the CT unit/s? Just before each core enters the isolator terminals and then house the Indirect Connection Meter in an empty CU enclosure on DIN rail?

Thanks again for all your help, I really find electrics interesting and would like to broaden my knowledge!
Kind regards,

Matthew
 
Cheers for you help guys. I fully realise I could call him today, which I have now done, but it never hurts to learn from these topics!

In response to old_sparky_RE, no it is not a caustic environment and yes there is no need to use SWA except for we can't find a HO7 equivalent any cheaper and I thought it was the industry norm to run SWA for industrial applications and sub-metering etc. But noted, and taken onboard :).

In regards to the CPC, we will run one with it in additon - for the price of 30 metres of single core 25mm we may aswell protect ourselves completely. Better to be safe then sorry and all that!

On the topic of industrial electrics, we are having to sub-meter this 160A supply, would I be right in saying that CT's would be needed as standard loop-in/out boards aren't available with ratings this high? If so is their a 'normal' place to site the CT unit/s? Just before each core enters the isolator terminals and then house the Indirect Connection Meter in an empty CU enclosure on DIN rail?

Thanks again for all your help, I really find electrics interesting and would like to broaden my knowledge!
Kind regards,

Matthew

exactly as you say ct's needed over 100a and fitted onto the cable as it enters the distribution board, then normally a 6a 3ph mcb to power the meter display and leads from ct's as per instructions
 
Excellent, thank you. I will wait and see if there is enough room before the cores enter the terminals of the isolator or if a seperate CT Chamber before this would be needed.

Last question if I may, the setup is as follows: 160A 3 Phase connection from the main electrical intake room connected to a spare 160A breaker already in situ. This will then feed through on cable tray to our UPS room where it will initially go into a TP&N fused isolator (hopefully with room for the CT's) and from here it will feed directly into the UPS. The output again is ~160A 3 Phase and we need to feed this into a distribution board to power each Single Phase 16A outlet in the main server room.

We will get an 18Way 3 Phase distribution board, and I have found a decent 3 Pole MCCB Isolator at a good price, but my question is will this fit into the board as it looks much bigger then a standard 100A/125A version. Is there a specific board for these or what happens here? The MCCB we are looking at is here.

Lastly, back to the CT's, the meter display as explained above, needs it's own 6A 3 Phase supply but naturally this is sited before the UPS with no CU, only a TP&N isolator in place. Where would you recommend we take power from in this scenario to power it?

Thank you again for your time, really appreciated.

Matthew
 
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Without the details of the DB and isolator it’s impossible to give an answer. I’d be reluctant to use a 2nd hand unit for this job.
As to the CT chamber I’ve usually used 3 back entry NIT fuse holders plus a back entry NIT neutral link mounted on the front of the chamber along with the meter.
The fuses being fed in double insulated singles from the isolator.

General layout

View attachment 5861
 
Hi Tony,

Apologies for the delay in responding. Just a quick message to say thank you for the drawings and explaining your usual installation setup to me, much appreciated. Will post pictures once the work has been completed.
Thanks again,

Matthew
 
Look forward to seeing how you go about it.
There’s no hard and fast way of doing it. With me it was a case of I inherited a lot of old switchboards, that was how they were done so I just carried on the same way.
 

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