Generator three phase connections / cables

[Hades]

Hi,

I have a 50kVA three phase generator. The installation is fascinating and I am interested in knowing what the electricians are taking into consideration when selecting the correct cable type. I dabble in low voltage electronics and circuitry and have a basic knowledge of the 17th Regs etc but am not a 'Qualified Electrician' and ask this question out of interest and the hope that I can lean something .

The rated output is 70A and I spec that the min spec for any cable would be 25mm Singles (Copper), running in trunking together with the bonding. The cable run from the interlocks / control cabinet (for the generator) is ~3 meters. Given the environment it is possible that the cable may be exposed to oil and possibly diesel (in an accidental spillage).

I but would like some advice on the cable choice for these 3 meter runs? Are there any specific regulations that would cover these environmental conditions - i.e Generators and minor oil contamination?

 

[Engineer54]

I hope that trunking isn't attached to the generators terminal/connection box!! Normal PVC cables are pretty much immune to any occasional oil and diesel fuel contact, not so much if it's benzine. Cable raceways should always be run in such a manner as to avoid any such accidental exposure....

Control wiring, if not of the same voltage as the generator output, should be in a sheathed multi core cable, and it's insulation rated equal or higher than the highest voltage present in cable run encloses, or be totally segregated and run in it's own raceway...

There are many special cable types, go to a recognised cable manufacturer's web site and check out the many types available, and their uses...

 

[Hades]

I hope that trunking isn't attached to the generators terminal/connection box!

No it is not . Also, the cable raceway is run to avoid accidental exposure. I hope that no one is using Benzine in the open air these days ...! ). I am looking at Tri-rated cable.

 

[Engineer54]

You could do, It's what we use a lot on considerably higher rated Gen-Sets, it's flexibility is advantageous for vibration considerations. ...but as i say normal PVC cables should be more than adequate for your needs in this situation.

There are turbine Gen-Sets out there, that use aviation fuel, which is virtually paraffin!! lol!!!

 

[telectrix]

yep, engineer, a lot of ppl don't know that jet engines run on paraffin. wouldn't like to try and run a piston engined plane on it though.LOL.

 

[Engineer54]

Don't know about the older prop engines, but the turbo props use aviation fuel too. It's not quite paraffin, it's a highly refined paraffin giving a higher octane level and lowering it's flash point for safety purposes with a few additives thrown in for good measure!!! Just don't ask me how, or about the chemistry involved!!! lol
That's the gist of what i was told by a company pilot anyway...lol!!!!

 

[yellowvanman]

Diesel can react with PVC. Only last week I was storing some cable (T&E) in a lockup and a muppet builder split a load of diesel over the drums, rang up the cables manufacturers technical support and basically if its not removed fairly quickly it will chemically react (so I'm told) so I had to condemm the cable - couldn't risk it!

 

[Engineer54]

I think they were just covering there arses Yellowvanman, it would take a bit more time than that, to react with the PVC sheath, to the point of rendering it unusable... Iv'e seen some right bodge-up installations around fuel storage where cables have been saturated in diesel for god knows how long. In one case, the cleaners went in and cleaned the place up, couldn't really see any detrimental damage to the cables sheathing. These were SWA cables mind, not T&E, and there is i think a difference in the PVC make-up. Rarely see T&E overseas to be honest, it's more of a UK style house wiring cable than anything you would find on projects...

 

[Knobhead]

I’ve never had a problem with diesel contamination on PVC cable. Some cable runs have literally been awash with the stuff.
The biggest problem comes with the vapour condensing in the control gear, add a bit of dust and wait for the fun to start.