mixed voltages in Altronix ALTV244 box

Hmmmmm... The PDF of the box shows me that it does.

There also appears to be a distinct seperation between the 24VAC side and the 24VDC side.

Personally, I wouldn't bother using this. You can fabricate your own fused power bus in seperate enclosures - one for DC powered cameras (with a good quality filtered power supply) and one for AC powered cameras. When you're doing large multi-camera jobs, it's been my experience that maintaining a far more distinct separation between "AC" powered cameras and "DC" units means fewer servicing headaches later on.

The provisions you are referring to may be those for general premise wiring that pertains (eg) to wall switch for AC wiring controlled by low voltage.

Current limited, low-voltage wiring falls under other Articles of the NEC including Articles 720 (

You're absolutely correct, Marc. Good call!! The one he's referring to isn't available to the NA market (because it's not UL listed). If he actually was able to obtain one, he shouldn't be using it.

I didn't spec the job or buy the parts, all I'm doing is putting it all together. The power supply seems to be commonly available here in NA.. does the lack of a UL listing mean it's not (supposed to be) allowed to be sold in the US?

Jim

Jim,

Among other reasons, one can sell things that would violate building codes if installed for a particular use in part because whether they conform to codes depends in part on their actual application.

As designed, the power supply would appear to meet the basic requirements of a source for Class 1 low-voltage circuits as per NEC Articles 720 and 725 which specify =< 30 volts and =< 1000VA. I don't recall what the isolation requirements are.

Since it is not _marked_ as Class 2, whether it electrically meets the requirements of Class 2 is moot. But a listed Class 2 can be treated as Class 1 even if it has lost its marking. But that in turn means that the wiring from it has to conform to NEC Chapter 3 requirements which are the same as for 'normal'

110 & 220 AC except, if I recall correctly, conductors as small as 18 AWG may be used but no smaller. Most Chapter 3 conductors have to be at least 14AWG.

But whether it will satisfy an inspector once installed is a different matter. If you know where it is to be installed, get a pre-installation opinion from the/an inspector ("Authority Having Jurisdiction" -- AHJ for short -- in the parlance of the NEC).

Don't take my word for it, ask your inspector ... Marc Marc_F_Hult

I can understand that .. what I was questioning was his statement that the power supply I mentioned isn't available to North America because it's not UL approved. It _is_ available, and I was asking for clarification because it seems that he was saying UL listed is required for sale in NA?..

On this job, I'm lowest man on the totem pole. This is an assumption, but as the engineer who designed the install and the lead tech doing this are both keeping their fingers in the job I'm sure I'll be advised long before an inspector makes their way here. I've only just started in this arena of work.. but it does look interesting, and I hope to go far with it.

Thanks for the response..

Jim

You are welcome. 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 ?!% ").

HTH ... Marc Marc_F_Hult

"Marc F Hult" wrote

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?

Perhaps he was looking toward future owners, who might believe the wire was

18 gauge just because the code says any low voltage wiring supplying power to a device should be at least that size.

The bottom line, as you imply, is that you *have* to satisfy the local inspectors to get them to sign, so just get used to their way of doing things, even if it doesn't make a whole lot of sense. Practical advice.

An alienated inspector can find a whole lot more wrong than one who isn't. In terms of dollars, it's probably cheaper to use the heavier wire than to argue and have to deal with further objections.

-- Bobby G.

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

It occurred after I sent this that someone might actually do this and get hurt.

DON'T.

Please consider this a thought experiment, not a physical one, with the observed result that a short length of 24AWG wire will become red hot and melt. A longer length of wire will become hot enough to start a fire but not melt.

... Marc Marc_F_Hult

As a quick aside.. the above makes sense to me. As with standard

120vac wiring, the wire size is not calculated from load current but from circuit protection... a 20a circuit breaker will use 14g wire (IIRC). Please correct me if I'm wrong.

Back to the power supply.. as there is no partiton between high and low voltage, and I don't really have a choice about using this particular power supply, can anyone suggest minimum (code) or better on how to properly hook this thing up?

Thanks,

Jim

and here I was about to unroll 1 kay feet of Cat 5 to see at what footage it goes from glowing to burn up..

20 amp circuit uses 12ga wiring; a 15 amp uses 14ga wiring. Remember, LOWER gauge means THICKER wire. You can use bigger wire on lower amp circuits but not thinner wire on higher amp ones.

From: snipped-for-privacy@bellsouth.net snipped-for-privacy@bellsouth.net

"Marc F Hult" wrote

Agreed. Even OSHA has standards:

_______________________________________________

Design Safety Standards for Electrical Systems: Special Systems -- OSHA Standard 1910.308 1

1910.308(c)(1) -- Classification. Class 1, Class 2, or Class 3 remote control, signaling, or power-limited circuits are characterized by their usage and electrical power limitation which differentiates them from light and power circuits. These circuits are classified in accordance with their respective voltage and power limitations as summarized in paragraphs (c)(1)(i) through (c)(1)(iii) of this section.

(i) -- Class 1 Circuits

(A) -- A Class 1 power-limited circuit is supplied from a source having a rated output of not more than 30 volts and 1000 volt-amperes.

(B) -- A Class 1 remote control circuit or a Class 1 signaling circuit has a voltage which does not exceed 600 volts; however, the power output of the source need not be limited.

(ii) -- Class 2 and Class 3 Circuits

(A) -- Power for Class 2 and Class 3 circuits is limited either inherently (in which no overcurrent protection is required) or by a combination of a power source and overcurrent protection.

(B) -- The maximum circuit voltage is 150 volts AC or DC for a Class 2 inherently limited power source, and 100 volts AC or DC for a Class 3 inherently limited power source.

(C) -- The maximum circuit voltage is 30 volts AC and 60 volts DC for a Class 2 power source limited by overcurrent protection, and 150 volts AC or DC for a Class 3 power source limited by overcurrent protection.

(iii) -- The maximum circuit voltages in paragraphs (c)(1)(i) and (c)(1)(ii) of this section apply to sinusoidal AC or continuous DC power sources, and where wet contact occurrence is not likely.

1910.308(c)(2) -- Marking. A Class 2 or Class 3 power supply unit shall be durably marked where plainly visible to indicate the class of supply and its electrical rating. (See 1910.302(b)(3).)

______________________________________________

I assume these are very much like the NEC and UL requirements. Since you clearly are an expert in the low voltage code requirements, can you tell me what they consider as a "Class 1 remote control circuit?"

In paragraph i-A) they discuss a top end of 30V but in B) just below they say "has a voltage which does not exceed 600 volts." Does that mean the voltage of the remotely controlled circuit? It's not clear to me.

In your example, without the "inherent" current limiting provided by Class 2 wall-warts, wouldn't the wire have to be externally fused or have some other method of preventing the CAT-5/battery scenario you hypothecated?

Correct me if I am wrong, but the whole point of requiring Class 2 wall-warts is that a dead short at the end of the cable will result in the wall-wart shutting down and not burning up.

The Class 2 specification issues are well-documented in the archives of this group and others, like:

news:sci.engr.electrical.compliance

I assume the NEC puts emphasis on insuring Class 2 use in the home because non-compliant wall-warts have been repeatedly found to be the "point of ignition" in housefires.

There are plenty of power supplies that have been recalled because of fire hazard here:

Agreed. But isn't dependable operation usually a by-product of following the code? It's a chicken-and-egg sort of thing. I agree, however, that operational aspects rarely concern the inspector beyond simple function (for instance: does a three-way switch installation actually work as expected?)

Since it's hypothetical, we'll never know, but I would suspect in some cases he would like to see if the device powered by the circuit actually came on.

I had a wiring harness fire in an old Ford LTD once. I was impressed by how much damage it did in a very short time. That was a long, long time ago and I imagine harness fires are far less common because there are a lot more fuses, fusible links and other protections on automotive electrical systems these days.

responsibilities of

It would be nice to think that he did understand, and was enforcing the larger gauge simply because that's what the code says. One would think the inspector *has* to know enough about the device or the power supply to know where the various provisions of the code come into play. When your inspector comes, does he ever check whether the devices function or does he simply inspect the "cold" wiring and device markings?

Which means, among other things, fuses or breakers to prevent the meltdown you posit below:

Agreed. As you mentioned in the beginning, the most important aspect of all this is ensuring whatever wiring you do in your home is not a potential fire or shock hazard. For me, that means making sure ever power wire is fused or otherwise protected as close to the power source as possible AND that you use Class 2 transformers as well, even though they should have such protection built-in. It's so easy to fuse 12V lines with automotive fuses that there's no reason not to overprotect everything.

Thanks for the info. I'm about to tackle putting a skeleton video system in the house capable of running for at least a few days from a large marine trolling battery. The problem is that DC voltage drops off pretty quickly so I need to locate the power supply close to the point-of-use. I may end up using two batteries just to avoid all the issues involved in transmitting DC power over a distance.

One of my CCTV transceivers that supplies power, audio and video over a single RG6 cable has a variable voltage AC to DC power supply that you can adjust to deliver 12V at the camera, but without DC-DC converters, there's no way to crank up a 12V battery's output quite so easily to account for the voltage drop over long distances.

-- Bobby G.

Yikes! An 'expert' in Code matters I am decidedly not ! ;-)

(I'm a scientist, not a regulator, but know enough about some parts of federal environmental laws and regulation to have a sense of what constitutes being an 'expert' in regulatory matters. )

A few months ago I posted a url to the draft 2005 NEC. It may still be available through waybackmachine.org It is also available for purchase for ~US$150 and will eventually be available at your local library.

Later ... Marc Marc_F_Hult