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  #61  
Old 12-15-2007, 08:26 AM
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Pro-Scapes Pro-Scapes is offline
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I agree with ya pete. It was damp out when I was working one time and I got a little zap. I guess thats what you get for not shutting the power off.

I got burned one time pretty bad when I was younger from a 7.2v RC battery at high amperages. Anything high amperage and bad connections is dangerous. There should be more regulation on LV lighting but you shouldnt need to be a full electrician for it. Respect the electricity and it will do what its supposed to do.
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Old 12-15-2007, 12:07 PM
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Originally Posted by Pro-Scapes View Post
I agree with ya pete. It was damp out when I was working one time and I got a little zap. I guess thats what you get for not shutting the power off.

I got burned one time pretty bad when I was younger from a 7.2v RC battery at high amperages. Anything high amperage and bad connections is dangerous. There should be more regulation on LV lighting but you shouldnt need to be a full electrician for it. Respect the electricity and it will do what its supposed to do.
Billy, you can't compare ac and dc voltage like this, dc voltage is much more severe and we do not work with it.

As for arching, you can put 16 amps on 12/2 wire with 12 volts, 15 volts, or 22 volts, it really doesn't make a difference. Amps are amps no matter the voltage. So that's not a good argument either. You can create just as much arch from a 10 volt system on smaller wire as you can on a 24 volt system. It's just a matter of knowing the rules and how to apply them.

The facts are, no one has ever been injured by 30 volts or less. This is why the NEC has placed this limitation in the code (411).
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  #63  
Old 12-15-2007, 08:25 PM
pete scalia pete scalia is offline
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Originally Posted by Pro-Scapes View Post
I agree with ya pete. It was damp out when I was working one time and I got a little zap. I guess thats what you get for not shutting the power off.

I got burned one time pretty bad when I was younger from a 7.2v RC battery at high amperages. Anything high amperage and bad connections is dangerous. There should be more regulation on LV lighting but you shouldnt need to be a full electrician for it. Respect the electricity and it will do what its supposed to do.
Excellent post Billy. That statement that nobody has ever been hurt from 30 volts or less is absolutely ludicrous and unfounded. I can't believe that some people would be so unscrupulous to suit their own agenda to perpetuate a statement like that. I would bet that even the slightest shock to someone with a pacemaker or a weak heart could be potentially fatal.
I'm sorry but it's not worth potentially harming someone over a landscape light system operating at higher than 15 volts.
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  #64  
Old 12-16-2007, 04:20 AM
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ChampionLS ChampionLS is offline
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It's not the voltage thats dangerous, it's the amperage at a specific voltage that can harm you. Low voltage lighting is regulated not to exceed 15 Volts at 25 amps as per UL1838. This is where they set the cap as a safety regulation. No secondary circuit should exceed 300 watts, because that equals 25 amps. The golden rule is 25 amps or 300 watts at whichever voltage you decide 12-15.

Can you be electrocuted from 300 watts/25 amps... most likely not, but you can definitely count on feeling the current from it. There is more of a burn hazard from short circuiting of wires then any type of voltage arch. It's best to have the power supply turned off when splicing, or if your hands are wet.
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  #65  
Old 12-16-2007, 10:20 AM
pete scalia pete scalia is offline
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It's not the voltage thats dangerous, it's the amperage at a specific voltage that can harm you. Low voltage lighting is regulated not to exceed 15 Volts at 25 amps as per UL1838. This is where they set the cap as a safety regulation. No secondary circuit should exceed 300 watts, because that equals 25 amps. The golden rule is 25 amps or 300 watts at whichever voltage you decide 12-15.

Can you be electrocuted from 300 watts/25 amps... most likely not, but you can definitely count on feeling the current from it. There is more of a burn hazard from short circuiting of wires then any type of voltage arch. It's best to have the power supply turned off when splicing, or if your hands are wet.
Isn't this exactly what I said in the post that Billy agreed to?
Though the higher the voltage the greater the buzz. UL chose 15V limit for a reason. Who am I to challenge them?

It's much easier to comply with an inspectors ruling (requiring UL rated equiupment) than to attempt to fight them. I've got much bigger fish to fry and I can get along just fine with 15V. If you are using a Good transformer that puts out constant power and is giving you 15v out of the transformer when you are fully loaded then there will be very rare occasion that you would ever need more power. Keep your transformers within 100' of one another on jobs and use a X-10, UPB or a 12V relay if you want them to trigger together. You'll get along just fine.
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  #66  
Old 12-16-2007, 02:21 PM
irrig8r irrig8r is offline
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Don't taser me Bro!
Interesting topical quote.....
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  #67  
Old 12-17-2007, 09:56 AM
steveparrott steveparrott is offline
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To clarify how amps and volts play into electric shock - The amperage that comes into play in an electric shock is based solely on the voltage of the source and the resistance through the body.

Current (Amps)= Voltage / Resistance (ohms)

Whether you are contacting a lighting circuit carrying 25 amps or 1 amp is irrelevant. Loads which are external to the through-the-body circuit do not affect the severity of the shock through the body.

The UL 25-amp limitation to the secondary circuits is entirely meant to prevent fire - it has nothing to do with electric shock.
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  #68  
Old 12-17-2007, 10:07 AM
steveparrott steveparrott is offline
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Originally Posted by pete scalia View Post
Excellent post Billy. That statement that nobody has ever been hurt from 30 volts or less is absolutely ludicrous and unfounded. I can't believe that some people would be so unscrupulous to suit their own agenda to perpetuate a statement like that. I would bet that even the slightest shock to someone with a pacemaker or a weak heart could be potentially fatal.
I'm sorry but it's not worth potentially harming someone over a landscape light system operating at higher than 15 volts.

Pete, with all due respect, I've spent days pouring through every engineering and safety database including OSHA, NIOSH and CDC records. I failed to find a single incident of serious injury from contact with any voltage below 30 volts. In addition to this anecdotal evidence, studies with animals and human volunteers confirm these statements on safety.

Your accusation of 'unscrupulous' behavior is more fairly applied to those whose agenda is to conflate the notion that low voltage is dangerous.
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  #69  
Old 12-17-2007, 12:00 PM
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The current is what kills but the volts get it there

I agree with Pete. The fact is the higher the voltage, the higher the propensity to penetrate the skin, allowing the current to travel through the body. The resistance of the skin is greatly diminished with contact with water, (in particular salt water {sweat}). The studies that Steve refers to both by Prof. Dalziel in the 1940's, and more recently by the IEC, both put the "let-go" threshold at 16mA which when considering the resistance of the human body at 1000 ohms (generally accepted as the impedance for hand to hand contact in saltwater wet conditions) translates into 16V as the maximum voltage. (Ohm's Law I=E/R or Amps=Volts/Ohms, 0.016=16/1000) This is reduced for women and children. It is further reduced if there is any break in the skin. 23V is the maximum for before severe pain and difficutly breathing. By limiting to 15V, the UL is eliminating the pain threshold.
Again, in the hands of a professional, higher voltages are safe, but the concern is for the general public.
Steve is correct that the 25A rating only serves to reduce fire hazzard, we just went through this with our local electrical authority who was trying to limit us to class 2 (5A) installations. Our point to them was that public safety could better be served by limiting voltage (currently at 30V) to 15V. This seems to be the direction we are going, but I'll keep everyone posted as to how the negotiations turn out.
JH
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  #70  
Old 12-17-2007, 12:09 PM
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INTEGRA Bespoke Lighting INTEGRA Bespoke Lighting is online now
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Quote:
Originally Posted by johnh View Post
I agree with Pete. The fact is the higher the voltage, the higher the propensity to penetrate the skin, allowing the current to travel through the body. The resistance of the skin is greatly diminished with contact with water, (in particular salt water {sweat}). The studies that Steve refers to both by Prof. Dalziel in the 1940's, and more recently by the IEC, both put the "let-go" threshold at 16mA which when considering the resistance of the human body at 1000 ohms (generally accepted as the impedance for hand to hand contact in saltwater wet conditions) translates into 16V as the maximum voltage. (Ohm's Law I=E/R or Amps=Volts/Ohms, 0.016=16/1000) This is reduced for women and children. It is further reduced if there is any break in the skin. 23V is the maximum for before severe pain and difficutly breathing. By limiting to 15V, the UL is eliminating the pain threshold.
Again, in the hands of a professional, higher voltages are safe, but the concern is for the general public.
Steve is correct that the 25A rating only serves to reduce fire hazzard, we just went through this with our local electrical authority who was trying to limit us to class 2 (5A) installations. Our point to them was that public safety could better be served by limiting voltage (currently at 30V) to 15V. This seems to be the direction we are going, but I'll keep everyone posted as to how the negotiations turn out.
JH
Great follow up post here John. I for one appreciate the attention to detail and the sources that you provide to support your posts.
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