I have been doing overseas work specified to comply with the NEC. We have been converting metric wire sizes to equivalent AWG sizes and then using the ampacity tables. We check our calculations with the manufacturer's ampacity and assure we do not exceed their rating. I believe that this meets the intent of the code but the question has come up "Does this actually comply with the NEC" Is the anything in the NEC or NFPA standards that specifically allow use of metric sized wire.
Metric wire sizes and the NEC
- Thread starter wickhamd
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kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I think you are going to be challenged to use overseas products, but design to NEC.
One thing to keep in mind, is that their equipment is rated differently, and also do short circuit calcs differently. The short circuit ratings of equipment do not compare at all with US methods and there is not a cross reference. There are many IEEE papers on this.
IEC breakers are all rated 100% so there is no 80% loading of circuits. The cable sizes as you have already determined do not align with US standard sizes. Are you going to actually purchase all US equipment, or are they going to buy cable and equipment locally? They will not be able to get AWG cable overseas, and therefore you have to use mm^2 sizing and ampacity.
I have an IEC cable Handbook from ANIXTER Wire and Cable, I would suggest you contact them or an IEC cable manufacturer to get cut sheets and so forth to use IEC cable sizes. Internet search may get you to the manufacturers webpage.
One thing to keep in mind, is that their equipment is rated differently, and also do short circuit calcs differently. The short circuit ratings of equipment do not compare at all with US methods and there is not a cross reference. There are many IEEE papers on this.
IEC breakers are all rated 100% so there is no 80% loading of circuits. The cable sizes as you have already determined do not align with US standard sizes. Are you going to actually purchase all US equipment, or are they going to buy cable and equipment locally? They will not be able to get AWG cable overseas, and therefore you have to use mm^2 sizing and ampacity.
I have an IEC cable Handbook from ANIXTER Wire and Cable, I would suggest you contact them or an IEC cable manufacturer to get cut sheets and so forth to use IEC cable sizes. Internet search may get you to the manufacturers webpage.
re: Kingpb
We generally use US equipment. Because of shipping weight and availability we use metric wire. We feel we are correct in conversions and sizing of the metric wire. The only issue is that because the NEC only addresses AWG sized wire specifically some people here are arguing that the NEC indirectly prohibits use of metric sized conductors. We have engineering support available and they support our calculations.
This may be more of a legal question than a practical question but I thought someone may have dealt with this issue and had an answer.
Thanks
We generally use US equipment. Because of shipping weight and availability we use metric wire. We feel we are correct in conversions and sizing of the metric wire. The only issue is that because the NEC only addresses AWG sized wire specifically some people here are arguing that the NEC indirectly prohibits use of metric sized conductors. We have engineering support available and they support our calculations.
This may be more of a legal question than a practical question but I thought someone may have dealt with this issue and had an answer.
Thanks
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