base board heaters

[Gerby]

I need someone to clarify 62-114 (4 a,b)for me.Lets say I have 3 b.b. heaters on a 20a breaker.1- 2000w 1 -1000w 1-500w.They all have wall stats fed with #12. The heaters are all less than 7.5 m from their respective stats.however I can only reduce the wire on the 2000w heater to #14 because it is less than 7.5m and more than a third of ocp.Where as the other 2 would have to remain #12 is this correct?

[yorky]

Rule 62-114 (a)(b) only requires that the tap conductors meet this requirment, therfore you would be able to reduce the wire size on the other two heaters, as they are both less than 7.5m and at least a third the ampacity of the o/c device.

[neil seidner]

Yorky: you are right, the tap conductor rule (14-100) does not apply, however if the tap conductor rule does not apply, the the 3m and 7.5m distance and the 1/3 ocpd are all irrelevant. The only rule that applies is 62-114 (7)(a)and(b), and the notwithstanding clause in 62-114 (8). Gerby: read 62-114 (8) carefully. My calculations are:

62-114(7)(a) 3500W/240V=14.58A

62-114(7)(b) 20A/80%=16A

62-114(8) for a #14AWG 15A*125%=18.75A

Since 18.75A does not correspond to a standard rating, you are allowed to use a 20A breaker to protect a #14 wire. You can use #14 for the entire circiut.

[Gerby]

In rule 62-114 (4a,b) I wasn't sure what they were refering to when they said 1/3 but I think I got it they are saying that the conducters ampacity cannot be less than 1/3 of the over current device right?

[neil seidner]

Sorry Gerby, I should have read you original question more clearly. 62-114(4)(a)&(b) would be used on a circuit larger than your example. Perhaps a circuit with a 60A overcurrent. You would use 62-114(7)&(8) to calculate the branch circuit size (cables feeding the stats). You could use, as small as, #12 AWG (#14 for a 45A OCPD) between the stat and the heater, provided the distance is less than 7.5m and the full load current of the heater is less than 20A. It seems as if the CSA has determined that, if there is a short, a short length of a smaller condutor will still allow the breaker to still trip safely.

<font color="#a62a2a" size="1">[ January 10, 2004 11:55 AM: Message edited by: ccrash ]</font>