SY cable current rating ??

[Buzz1980]

Hi All

got a question regarding SY cable. I have tried to find the current rating for 6mm SY cable and have found a data sheet the GEM cables which states 33 amps in conduit thermal wall and 54amps when in free air. Also seen a few other manufactures state these ratings but a lot stating 44amps for 6mm cable. What table is best to go with in BS7671 to suit this cable. Reason being have a site transformer with a pull of 40 amps have installed this on a 40amp type D MCB to suit the transformer. But didn’t take into account the difference in current rating from SWA , T&E and SY cables ? Hope that makes sense ? any info will be much appreciated

 

[Buzz1980]

Also have noticed that SY rated at 70 degrees op temp ?

 

[Strima]

SY isn't recognised by BS7671 as it isn't manufactured to any recognised British standard. You would need to consult manufacturers data.

Also it's use is classed as a departure from BS7671.

 

[Buzz1980]

Hi strima

Thanks for the reply. Ok will consult with manufacturer. Too be honest might just go with the general rating of a 6mm SY cable that I have been seeing rating it at 44amps. This install is in free air on its own and only 10metre run so I think the 6mm will be good to go on a 40amp MCB to protect the cable. Have seen other tables state that there SY cables are rated for 54amps in free air ?

 

[Buzz1980]

See loads of SY install feeding lights, motors etc in industrial plants all the time ?

 

[pc1966]

It is a perfectly good cable to use for many things, but it is not a recognised UK standard for "fixed wiring" and similar. So if used you should consult the manufacturer of the cable for precise data and note that in any documentation relating to the design and testing.

And yes, that means multiple manufacturers with possibly different specs if you have different brands in use. Sadly that is the consequence of it not being a formal standard.

 

[Buzz1980]

Yeah noticed that but seen it all over must have comments in the test sheet for using SY instead of SWA. I mean I can’t see the current rating of the SY being much less than a standard T&E ?

 

[pc1966]

It is very unlikely to be less as T&E assumes a max of 70C for PVC insulation. So if you start with that I don't see it as a risk.

 

[Buzz1980]

Yeah have looked through different manufactures. Some just state 44 amps but some state 33 amps in conduit and 54amps in free air for 6mm SY so even taking it from T&E spec then I will have 47amps free air which is more than enough. So can protect the 6mm SY with 40amp MCB. ? ?

 

[pc1966]

6mm in conduit is down to 32A MCB protection, but if your SY is in free air then 40A would seem perfectly reasonable (assuming it is not a hot environment near an oven, etc).