- Is there an authoritative source of information for the ampacities of conductors that are used in other countries and that are manufactured in metric sizes?
- Put another way, are there tables that are equivalent, in metric sizes, to the NEC tables 310.16 and 250.122?
- Do you think the selection of EGC sizes (as displayed in table 250.122) was based on the ampacity of the conductor that will serve as the EGC?
I am reviewing the design for a project at a military base in a mid-east country. I made a comment that noted that a 30 amp circuit only had a 4 mm2 EGC (close to our #12), and saying it should be 6 mm2 (close to our #10). The design engineer responded that the ampacity of a 4 mm2 was close to that of a #10, so it should be fine. I am inclined to disagree, because when the EGC is doing its job, the wire's ampacity is not the important factor.
Thoughts?
The British Standards differ in terms of accepted practices-- as applied to electrical installations that will corroborate with their building designs.
For example: There is a limit on the number of outlets for a specific area. If the area exceeds 100 m2, you need to have two branch circuits.
This requirement is noted on their BS 7671. This BS standard is the equivalent to our NEC.
It covers a wide range of guidance unlike the NFPA.
Now, that is just one quirkiness to the British Standard.
You alluded to the British version of codes. . . yes, they do follow codes, their own codes.
The ampacity of conductors [and you know this already] is dependent upon the cross-section of the conductor.
Whether the cross-section is expressed in mm2 or AWG, the ampacity would remain dependent on the thickness of the wire.
The apprehension towards the engineer's nonchalant: "it would be OK " to use a smaller conductor for a 30 Amp Circuit breaker-- doesn't bode well with us gringos with our "fanatical" adherence to our NEC.
The Middle East countries use the BS 7671 wiring standard. There is no NEC there.
The reason the engineer say that 4mm2 is acceptable is:
Branch circuits for receptacle (plugs) are wired with MAIN RINGS. This is a system not allowed in NEC but is common in countries with deep British influence.
MAIN RINGS--if wired properly have a certain advantage over North America's RADIAL SYSTEM.
As mentioned: "if wired properly" also offers a safe wiring. British electricians are more than capable of wiring things properly. They command respect in the community.. .a noble job indeed.
MAIN RING system allows a smaller wire size, not only that these countries operate at 240 volts , 50 hz.
Voltage and frequency are irrelevant in this discussion at this point-- we are concerned of current that would flow through the conductor.
The MAIN RING system is wired that originates from the circuit breaker to the receptacles (plugs) that are daisy-chained and then continues back to the same circuit breaker.
I didn't cover the neutral because it's not protected by the CB.
Picture a closed loop that completes a circle that ends where it started.
So, basically you have two wires ( one going out and one coming back) that are feeding a group of outlets from a common circuit breaker.
You have two wires serving as home run for one single branch circuit. This is the reason why you can get by with smaller wires.
Australia uses the British Standard and Malaysia and Singapore too.
While on vacation I helped wire my sister's house remodel in Melbourne-- almost ten years ago.
Brother in law is a building contractor.
Google BS 7671 for British wiring regulations.
I also suggest verifying whether the British MAIN RING is used since Corps of Engineers are involved on the project.
