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  #11  
Old 11-25-2013
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Re: Air Conditioner Hazard Potential

Quote:
Originally Posted by ebs001 View Post
We are not talking a short here but a closed circuit on the control side.
Of course we are talking about a short circuit. The question is why the discharge line that the wires shorted against wasn't grounded.
Quote:
The control wire closes the fan relay and the fan will then get constant power just the same as switching the fan switch to on on the thermostat.
Yes, if we were talking about a short between R and G on a thermostat circuit that would be the result, assuming that the metal that completed the circuit wasn't grounded. My understanding from the original post was that it was a power cable that was damaged not a thermostat wire.
Quote:
Short circuits cause breakers to trip not fans to run. 24 volt control circuits do not have fuses nor is the control transformer grounded on the load side.

The neutral is never switched.
A short circuit is something that causes current to flow through a path other than it's intended one. If the short takes a path that allows excessive current flow, such as to ground, then breakers trip, fuses blow or wires burn up.
24v control circuits usually do have fuses, or a breaker on the transformer, at least on land! If they don't, then in an over-current situation the transformer and/or the wiring will burn up. (usually the transformer) If the control voltage is being switched through a circuit board it will destroy the board. That is why there will usually be a fuse on the control board.

I am aware that the neutral should never be switched but I have seen it done due to incorrect field wiring and general incompetence.

The scenario that you put forth that the stat wire hot shorted to the fan wire is a plausible one, and makes more sense than the idea that the line voltage wires shorted together, as the OP stated.

My point is that the copper discharge line that apparently provided the new circuit path SHOULD have been grounded, and whether you are talking about 24v or 115v the current should have taken that path to ground as the path of least resistance. If that pipe is not grounded then it is extremely dangerous because in the event of an electrical failure such as the one we are talking about, that piece of equipment could become energized and stay that way until some unsuspecting person touches it and creates a path to ground through their body! That is no big deal if we are talking about 24v, but with 120v it could be fatal!
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  #12  
Old 11-25-2013
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Re: Air Conditioner Hazard Potential

SchockT, your definition of a short circuit is wrong. A short circuit bypasses the load by providing a minimal resistance path. In this case the load was not bypassed. The load side of 24 volt transformer is rarely if ever grounded. Therefore there can be no path to ground to complete the circuit if one of the conductors, in this case R, touches the copper tubing. Even if the transformer were fused it would not blow the fuse as no over current situation existed.

While you may have seen neutrals switched, it's note a very likely scenario in a manufactured product such as a marine air conditioner as they would not receive UPL or CSA approval.
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Old 11-25-2013
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Re: Air Conditioner Hazard Potential

Is this wiring issue from the install or is it factory and integral to the unit? If it is factory, what brand is the unit so other owners can check this issue? If it from the install, maybe a sleeve over the wiring would do the trick to prevent the chafe/melt problem.
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  #14  
Old 11-25-2013
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Re: Air Conditioner Hazard Potential

While I don't make the assumption that ShockT mades about it being DC voltage, nor a neutral switch, I was thinking something similar about the 3-wire. That is either a hot, neutral and ground or has been set up to switch one side of the the circuit, typically the hot side.

If a switching setup, I can see the a short would close the circuit and power whatever it was switching. Although, it seems odd it would only be switching the fan and not the entire unit. Perhaps a closed thermostat in this scenario is why only the fan powered up.

If it was the AC power supply, I don't see how a short would have powered anything and more likely would have tripped a breaker/fuse.
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  #15  
Old 11-25-2013
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Re: Air Conditioner Hazard Potential

Guys--

Firstly, thanks for the interest. Secondly, keep in mind that I am "challenged" in matters electrical so my use of terminology or descriptions may leave something to be desired. N'any case, to clarify, the power cable to the fan assembly is 120v. The green wire in that cable is connected to the fan assembly on one end, and to a neutral green bus board on the Air Conditioner ("AC") controller circuit board. The black and white wires in that cable are connected to either side of a variable voltage relay (kind of a digital rheostat) on the circuit board in the control module that, depending upon the difference between the ambient air temperature and the thermostat setting, varies the fan speed from very slow (when there is little temperature difference) to full bore (when there is a 10º or greater difference). The 1/8" dia (or so) compressed gas line that melted the insulation (and one of my slip neighbors, a mechanical engineer who owns a sizable AC contracting firm assures me that such a line can get hot enough to melt insulation) merely acted to complete the circuit between the black and white wires in the cable, activating the fan, just as the switch on the circuit board does/would when it is enabled. (I believe there is a separate "hot" red colored lead to the fan assembly as well.)

The air conditioning system on our boat is identical to its predecessor, which we had for 16+ years, in all respects save for the control module which is now digital verses the earlier analog system--i.e. manual controls of fan speed, heat or cooling selection, etc. (Frankly I prefer the old arrangement to all of this digital BS). The old unit worked extremely well so when it died of old age, we replaced it with it's newer, supposedly more up-to-date sibling.

The power cable to the fan assembly came in contact with the hot coolant tube because of the failure of a wire tie that was used to route the cable around and past the compressor assembly; and, because the coolant tube was not enclosed in an insulating cover (although my slip neighbor indicated that wasn't unusual either). The foregoing, and the compactness of the system which brings potentially conflicting mechanisms in close proximity to one another gave rise to our problem. The make of the machine is irrelevant as I have since observed the same proximities and prospective conflicts/hazards in two other systems, made by two other, different, manufacturers, while helping neighbors check their systems as I suggested others do of theirs in my original post. And, the builder of our machine is issuing a technical bulletin on the matter that is being sent to the owners and installers that handle its machines so that corrective/preventive measures and be taken, if necessary. I am afraid naming the manufacturer would simply cast it in an undeserved bad light, which I prefer not to do, especially considering the lengths the company went to helping me resolve the issue at no charge and with only moderate inconvenience.

FWIW...

Addendum: Since posting the above message I have learned that the red wire referred to in the parenthetical phrase at the end of my first paragraph, above, has nothing to do with the operation of the fan and is merely coincidental to the 3-lead power cable. Please see my follow-up post, #20, below.
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Last edited by svHyLyte; 11-25-2013 at 04:04 PM. Reason: Add addendum; add second addendum
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  #16  
Old 11-25-2013
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Re: Air Conditioner Hazard Potential

Svhylyte,

I agree that the manufacturer should not be blamed for such a failure. That kind of thing can happen on any make of equipment. If anyone is to blame for the problem it would be the installer who didn't make sure the wiring was correctly routed and secured before walking away from the unit.
The only reason I would like to know the make and model of the unit is so I can dig up a wiring diagram to satisfy my own curiosity about how that happened without blowing a breaker, or causing more damage.
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Old 11-25-2013
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Re: Air Conditioner Hazard Potential

Quote:
Originally Posted by ebs001 View Post
SchockT, your definition of a short circuit is wrong. A short circuit bypasses the load by providing a minimal resistance path. In this case the load was not bypassed. The load side of 24 volt transformer is rarely if ever grounded. Therefore there can be no path to ground to complete the circuit if one of the conductors, in this case R, touches the copper tubing. Even if the transformer were fused it would not blow the fuse as no over current situation existed.

While you may have seen neutrals switched, it's note a very likely scenario in a manufactured product such as a marine air conditioner as they would not receive UPL or CSA approval.
No, my definition of a short circuit is not wrong. 24v control transformers are almost always grounded, but even if they aren't, if you touched the hot side to ground the electrons would take that current path.( We are not talking about a battery circuit here!) And you could easily end up with a scenario where the neutral side of a circuit is being switched. It could be as simple as the installer reversing the wires when he connected the power to the unit.

But what do I know, I have only been working in the Refrigeration/HVAC trade for the past 20 years!
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Old 11-25-2013
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Re: Air Conditioner Hazard Potential

Looks in... reads... is thankful there hasn't been any recent boat fires on Tampa Bay... goes back to her woodworking bench project.

guys and their shorts....
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Old 11-25-2013
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Re: Air Conditioner Hazard Potential

Quote:
Originally Posted by SchockT View Post
No, my definition of a short circuit is not wrong. 24v control transformers are almost always grounded, but even if they aren't, if you touched the hot side to ground the electrons would take that current path.( We are not talking about a battery circuit here!) And you could easily end up with a scenario where the neutral side of a circuit is being switched. It could be as simple as the installer reversing the wires when he connected the power to the unit.

But what do I know, I have only been working in the Refrigeration/HVAC trade for the past 20 years!


The only explanation that makes sense is that the fan relay was energized powering on the fan.

From the OP's explanation above it sure sounds like he is talking about the control circuit with red, green, black and white wires mentioned as going to the fan assembly. The black wire coming in contact with the copper would cause a short circuit if it was 120 volts.

BTW here is the definition of a short circuit from the on line free dictionary

(Electronics) a faulty or accidental connection between two points of different potential in an electric circuit, bypassing the load and establishing a path of low resistance through which an excessive current can flow. It can cause damage to the components if the circuit is not protected by a fuse.

I was unable to find anywhere that said a short circuit was just an alternate path. Maybe HVAC guys have their own definition that is different than the rest of the world.

X1 or X2 of the 24 volt transformer has to be grounded in order for the hot to cause a short to ground. You are without question wrong in that regard.

Last edited by ebs001; 11-25-2013 at 02:10 PM.
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Old 11-25-2013
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Re: Air Conditioner Hazard Potential

Quote:
Originally Posted by ebs001 View Post
The only explanation that makes sense is that the fan relay was energized powering on the fan.

From the OP's explanation above it sure sounds like he is talking about the control circuit with red, green, black and white wires mentioned as going to the fan assembly. The black wire coming in contact with the copper would cause a short circuit if it was 120 volts.

BTW here is the definition of a short circuit from the on line free dictionary

(Electronics) a faulty or accidental connection between two points of different potential in an electric circuit, bypassing the load and establishing a path of low resistance through which an excessive current can flow. It can cause damage to the components if the circuit is not protected by a fuse.

I was unable to find anywhere that said a short circuit was just an alternate path. Maybe HVAC guys have their own definition that is different than the rest of the world.

X1 or X2 of the 24 volt transformer has to be grounded in order for the hot to cause a short to ground. You are without question wrong in that regard.
Subsequent to my last post, I have spoken with the engineers at the AC Maker. The red wire I observed is near to, but has nothing to do with the fan assembly. The white and black cables are 120v and power the fan. The copper tube that temporarily connected these wires merely completed the circuit in place of the connection normally made by the fan speed control module on the circuit board which was inactive in the event. The insulation on the green "neutral ground" cable was damaged but not fully compromised and so not involved in the event.

FWIW...
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