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Posted By Topic: Cable Grouping and the impact on electrical instal

Feb 17 2019 12:44

Cable tying conductors versus not cable tying within a switchboard.

An interesting video (UK) of what happens when we tie conductors together.

Feb 17 2019 16:27

Can you just give us the executive summary?
I don't have 26+minutes to listen to him waffle on about UK rules.

Feb 17 2019 19:56

Doug, no.

Feb 17 2019 20:58

AS/NZS 3008.1.1.2017 3.5.2

Feb 17 2019 21:05

Particularly AS/NZS 3008.1.1.2017 (B)

Feb 20 2019 18:24 might have something to say about that in many switchboards, though.

Should also really be reading from 3008.1.2; 3008.1.1 is for Aus.

Not to mention that many circuits are sized for TPS buried in insulation, not singles in a switchboard.

For example, 2.5 singles in air (spaced) are rated for about 33A (Table 4). Add the derating factor for 6+ circuits (so 12 singles in each bundle, so 12 circuits total) of 0.67 (Table 22) and we're still at ~22A (1.5 at 16A).

You could consider that this is in a switchboard and might be >30C, but you might also be able to claim diversity in that you can't load all circuits to 100% without tripping the supply fuse. I am not sure if that's a rule anywhere.

Could also argue that, as this is V-90, we may be able to run at 90C. I'm not sure if breakers etc. are rated for those conductor temperatures, but there should be little impact from mechanical damage so the other conditions should be satisfied.