| phil-news-nospam@ipal.net 2005-06-24, 6:25 pm |
| On Thu, 23 Jun 2005 16:07:59 -0500 Bud <remove.BudNews@isp.com> wrote:
| HorneTD wrote:
|
|>
|>
|> Phill has a point. 210.21 (B) (3) would not appear to apply to branch
|> circuits that only have one outlet. I strongly suspect that was not
|> what the code making panel intended but the way 210.21 (B)(1) reads now
|> you could put a twenty ampere receptacle as the only outlet on a fifteen
|> ampere circuit.
|
|
| Hard to believe but apparently true. A single outlet just has to have a
| higher rating than the branch circuit. Not only can you put a 20 amp
| single receptacle on a 15 amp circuit you can put a 30 amp, 100 amp ....
|
| This appears to have been in effect at least back into the 1980s.
|
| One way to see check the reasoning behind a code item is to look for
| proposed changes and see how the code making panel responds. There were
| no proposed changes to this rule as far back as 1983 (1996 and 1993 are
| unknown). This rule was invisible?
There may have been _other_ rules in place that negated the bad effects
of this rule. Note that 210.21(B)(1) allows either an equal rating or
a higher rating on the single outlet. Another rule could prohibit the
higher rating, resulting in only allowing an equal rating when both
rules are in effect together. The other rule may have existed in the
past and then was removed.
HOWEVER, the issue is not as simple as that. What if the appliance that
needs a dedicated circuit requires 25 amp overcurrent protection, where
20 amps is too low (will trip) and 30 amps is too high (could allow a
long term overheating issue). You can put in a 25 amp breaker easily
enough. But what size of receptacle do you use? A 20 amp one is too
small. A 30 amp would would be safe in that it should not burn up with
25 amps used through it. What 210.21(B)(1) does is allow use of the
30 amp outlet.
What I think the rule should be change to is that for a given circuit
rating, the only outlet allowed is one with a _configuration_ equal to
the circuit rating for circuits matching a configuration, or the next
higher configuration where a matching one is not standardized. Thus:
circuit outlet
10 amp 15 amp (I think 10 amp is still allowed on dedicated circuits)
15 amp 15 amp
20 amp 20 amp (maybe use 20-amp only outlet)
25 amp 30 amp
30 amp 30 amp
35 amp 50 amp
40 amp 50 amp
45 amp 50 amp
50 amp 50 amp
55 amp 60 amp
60 amp 60 amp
etc
Such a code change should reference NEMA standards for outlet configuration.
Then a 30 amp outlet would be allowed on a 25 amp circuit, but a 50 amp
outlet would not be allowed. I think we all (even Roy) would agree this
is the way it should be.
One thing I think the code needs to do is distiguish with better terminology
the difference between the current capacity rating of a device, and its
configuration with respect to the standard plugs it will accept. NEMA X-15R
devices do (now days) have a current carrying rating of 20 amps. As long
as appliances plugged in are unlikely to create overcurrent situations of
more than their own cord-and-plug rating without exceeding the 20 amp trip
current, things are safe allowing receptacles on 20 amp multi-outlet circuits
that accept 15 amp plugs. The 20 amp configuration accepts 15 amp plugs, so
there is no new hazard in this regard by installing a receptacle that refuses
to accept 20 amp plugs. You can get 20 amp receptacles that do refuse 15 amp
plugs, and that can be useful on single outlet circuits.
--
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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