Re: Inspections: (was Re: mixed voltages in Altronix ALTV244 box)

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Sat, 3 Dec 2005 22:31:48 -0500, "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>
wrote in message  <85KdnWTs1NCx_g_enZ2dnUVZ_tCdnZ2d@xxxxxxx>:

>"Marc F Hult" <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote
>
><much stuff snipped, subject line modified>
>
>> Sometimes the less one knows technically, the better one is
>> able to cope with regulatory requirements  -- a hopefully gentle way of
>> implying that if the engineers and other techs you work with are not
>>familiar  with the NEC, they may find it counterintuitive. ("The circuit only
>> needs 50 mA of 12vdc but the inspector says we have to replace all the wire
>> we ran with at least 18 gauge conductors inside conduit ?!% ").
>
>A very interesting subject, indeed, since so much of HA involves almost
>every "inspectable" area of the home.
>
>Do you think the inspector in the above (hypothetical?) case understood the
>lower than normal current consumption issues?
>
>Or was he more concerned with blind obedience to low voltage code
>requirements?


IMO, what folks that do their own home automation and other low voltage
installations in the US and Canada need to grok is that the NEC, NFPA, UL and
ULC address fire and electrocution prevention. They do not, and are not
intended to insure dependable or efficient operation of electrical devices or
to protect those devices in case of malfunction or misuse.

So in the hypothetical I posed, the concern of the inspector is not whether the
wires would perform under normal operation, but rather what hazards would be
created during abnormal circumstances and how to minimize their impact.
(Connect a length of twisted pair of CAT5 to a car battery and short the far
ends if you want a hint of what "low-voltage" can do.)

So the fact that 18 AWG is much larger than is needed for the power
requirements of any given device is quite irrelevant to the responsibilities of
the inspector. And so whether he understands that or not is also not important.

What matters is that if a device is not marked as Class 2 (as all the wall
warts in your house _should_ be), the National Electrical Code that he is
enforcing *requires* it to be treated as if it did not have Class 2 intrinsic
power limitation  and so would need to be treated (at least) as Class 1 (=< 30
volts and =< 1000VA with related higher wiring requirements) in order to assure
safety to people and property according to the Code.

Consider my CAT5 + car battery example:  it is clear that how much power is
drawn by the gizmo attached to the other end of the CAT-5 has nothing
*whatever*  to do with how safe the combination of power source, overload
protection and wiring is or is not.

HTH ... Marc
Marc_F_Hult
www.ECOntrol.org