Warranty inspections

[Marc D. Shunk]

Originally Posted by wsiegel

Is it true that they are addressing voltage drop in the 2008 NEC??

I hadn't heard that before, so I just did a search of the document for the words "voltage drop". It seems like that still appears in all the same places. A bunch of fine print notes (which aren't enforcable code text) and for Sensitive Electronic Equipment (stuff on the load side of isolation transformers) and for fire pumps. I didn't note any new appearances of that phrase in the '08 NEC in any of the enforcable text portions. The phrase occurs 26 times in the '02, '05, and occurs 28 times in the '08. I'm not into it enough to find where the two extra times in the '08 are at exactly.

[Robert J. OConnor]

HI's don't enforce codes, and therefore are not limited to comment on only enforceable sections of the NEC. So you can write up a high VD as a defect or a concern, just base on industry accepted standards or an FPN from the NEC, to be further evaluated or repaired by an electrical professional.

[Marc D. Shunk]

Originally Posted by roconnor

HI's don't enforce codes, and therefore are not limited to comment on only enforceable sections of the NEC. So you can write up a high VD as a defect or a concern, just base on industry accepted standards or an FPN from the NEC, ...

Nobody's asking you to enforce code. The load that is applied during the VD test is the point of concern. It's just silly. The VD observed during a 15 amp load test is neither standard or realistic for a dwelling. It is neither a safety issue, a nuisance, or a defect.

[cgoyette]

Originally Posted by Marc D. Shunk

You seem to not understand how voltage drop works, so I'll try to break it down for you.

You will have little to no voltage drop at low loads. The SureTest puts a 15 amp load on the circuit to measure that drop. At half that load, the voltage drop would be much, much less. At the load that a printer, for instance, puts on that circuit, the voltage drop wouldn't be anything to even talk about. The amount of voltage drop is directly proportional to the connected load.

Here's a little chart that shows how much #12 you can run various distances for various loads if you're interested in maintaining 3% vd.:


There is absolutely no way to know how a receptacle will be used in a home, so the application of a 15 amp load to calculate voltage drop is dubious at best.

I think you missed my point, I get Voltage Drop. Your explination was good though.

I am saying the transformers seem to hate low voltage and they get hot. I don't know why so if you could explain that it would be real helpful. In my other home upstairs 101VAC and once 98VAC (its some distance from the panel) (and the power in to the house is somewhat low at times 112VAC) the printer was wacky so I moved it down stairs with more that 110VAC and it worked fine.
The one thing I noticed was the transformer gets hot. In this house I have a detached garage and its low, the kids toys that have transformers to charge battery's seem to get hot also, however not so when charged in the main house.

Grounds are good, polarity is good, just low voltage 100VAC area.


So what would cause this? I also read that voltage range should be 110-125VAC but I think the transformers have some leeway in that.

Added info-The wires in and the wire out do not seem to change in temperature regardless of VAC.

Curt

EDIT add: I think where It got confusing is I was talking low voltage period, the example was under a load. I should have been more clear.

[Michael Larson]

Originally Posted by cgoyette

..........I am saying the transformers seem to hate low voltage and they get hot. ......

Curt,

Your photo is not a transforemer type(linear) power supply.

How hot is hot?
When tested under all rated voltage inputs, accessible surfaces of these devices are limited to a maximum temperature adjusted for 40 deg C(104 F) ambient.

I would check with your power company and ask them what voltage they are supposed to provide to your residence. The problem may lie with them.

[cgoyette]

Originally Posted by mlarson

Curt,

Your photo is not a transforemer type(linear) power supply.

How hot is hot?
When tested under all rated voltage inputs, accessible surfaces of these devices are limited to a maximum temperature adjusted for 40 deg C(104 F) ambient.

I would check with your power company and ask them what voltage they are supposed to provide to your residence. The problem may lie with them.

Mike,

My nomenclature was off and your are right. I will ask the power company at the lake whats the power in suppose to be. This may be like herding cats though, Santee power and Electric Coop is not known for being coopertive...pun intended.



Curt

[Mike Whitt]

Originally Posted by cgoyette

I am saying the transformers seem to hate low voltage and they get hot. I don't know why so if you could explain that it would be real helpful.

A transformer will work at any voltage. If I had a two to one transformer it wouldn’t care what voltage was applied it would simply give me a two to one voltage; 240 to 120 or 200 to 100 or 100 to 50 or 50 to 25 and so on. This is not true about autotransformers as they work just a little different than a regular transformer.
The insulation of the windings would regulate the maximum amount of voltage that could be applied.

If anything the transformer would produce less heat at a lower voltage than at a higher voltage. The same is true with resistive loads, the lower the voltage the lower the temperature of the device.

A simple experiment; wire a 40 and a 100 watt light bulb in series. Which bulb is the hottest? Did either bulb get as hot as it would if it were wired by itself?

We must remember that the voltage drop across any circuit or any branch of a parallel circuit will equal the voltage applied. In the experiment with the bulbs we designed a circuit that will have different voltage drops at each bulb. The total of the voltage drops will equal the total amount of the applied voltages. The lower voltage caused the 40 watt bulb to burn dim and not as much heat was produced by this bulb as would have been should it have been wired on a circuit by itself. The 100 watt bulb did not emit any light nor any heat.

Once again, voltage drop is NOT a safety issue but IS a design issue.

If it was such a safety issue it would be addressed in the rules of the NEC and the IRC which it is not mandated by either.

[Robert J. OConnor]

Originally Posted by Marc D. Shunk

It's just silly. The VD observed during a 15 amp load test is neither standard or realistic for a dwelling.

Connecting power tools like a heavy SawsAll via an extension cord or running a large hair dryer on a circuit that already has some general draw sure will get loads up around 15 amps.

Originally Posted by Marc D. Shunk

It is neither a safety issue, a nuisance, or a defect.

At a 3% to 5% VD I would probably agree. However very high VD on a circuit could indicate such things as a loose connection, which sure is a concern.

I don't subscribe to the practice of using specialized tools like a "circuit analyzer" for a home inspection ... but for those that do I understand and agree with why they would report very high VD. The question that I always ask is not whats the purpose, but where do you realistically draw the line between what is normal and what is a concern.

JMO

[Mike Whitt]

Originally Posted by roconnor

Connecting power tools like a heavy SawsAll via an extension cord or running a large hair dryer on a circuit that already has some general draw sure will get loads up around 15 amps.

Has anyone using a long cord on a Saws-All ever set a house or saw service on fire before? What normally happens? Saw gets hot and the breaker trips. Where is the danger?

As to the hair dryer and some other draw what would happen? The breaker would trip so where is the danger?

Would these things be inconvenient? Yes.
Would they be dangerous? No
It would all be a design issue not a life safety issue.

Originally Posted by roconnor

but where do you realistically draw the line between what is normal and what is a concern. JMO

I would recommend using something like this and if it lights up correctly move on to the next device

.

What I wouldn’t be doing is trying to design the electrical system after it has been installed.

Think about the old farm house that was built back in the 40s and 50s that have a service drop so long that they are only getting around 110 to 115 volts at the meter. Where do we stop doing the voltage drop test?

[Marc D. Shunk]

Bottom line... voltage drop causes no problems in a dwelling. This nonsense about electronics and transformers is a mere strawman tactic. Voltage drop in a dwelling is hardly ever measureable with the loads commonly applied in a dwelling, and when the receptacle is loaded, the minimal drop from domestic appliances causes no problems. The reports of problems due to "voltage drop" are anecdotal, at best. The SureTest is an interesting gadget, so feel free to report it's findings. It keeps me certainly employed, and makes me money. Just don't take it too hard when I report back with my professional opinion that no problem exists. It's probably worth reporting voltage drop for the 1 time in 50 that it might be due to a poor connection. Loose wires cause fires.

[rdawes]

An 18% voltage drop at 15 amps is about 324 watts. If that is linearly distributed in a #14 wire that is a long run then it is indeed not a safety hazard. If it is concentrated at a bad backstabbed outlet connection then it can get pretty darn hot. I have a 250 watt soldering iron that does quite well at generating enough heat to solder small copper tubing.

As a HI, I don't know which situation is present. So I opt to be safe for my client and recommend that at a minimum that the backstabbed outlet in question be hooked up to the screws.

10 years ago my wife was vacuming and said '"there's smoke coming from the outlet the vacumn is plugged into." It was a backstabbed outlet with a bad connection and very hot. The vacumn pulled about 10 amps. Excessive voltage drop can be a hazard. Not all the time certainly but once is enough.

[Mike Whitt]

Originally Posted by rdawes

An 18% voltage drop at 15 amps is about 324 watts. If that is linearly distributed in a #14 wire that is a long run then it is indeed not a safety hazard. If it is concentrated at a bad backstabbed outlet connection then it can get pretty darn hot. I have a 250 watt soldering iron that does quite well at generating enough heat to solder small copper tubing.

Should you have a voltage drop 18% on a 120 volt circuit it would burn a motor up before it would heat a loose connection to the point of a fire. If it is a lose connection such as you point out in the statement then it is not a voltage drop problem but a mechanical problem.

The formula for voltage drop is VD = 2 x K x Q x I x D/CM
“VD” = Volts Dropped
“K” = Direct Current Constant
“Q” = Alternating Current Adjustment Factor: The "Q" adjustment factor is determined by dividing alternating current resistance as listed in NEC Chapter 9, Table 9, by the direct current resistance as listed in Chapter 9, Table 8.
“I” = Amperes:
“D” = Distance
“CM” = Circular-Mils
I don’t see any thing in this formula that allows for loose connections such as wire nuts or push-in type connections. Voltage drop is nothing more than the resistance of the conductor that is carrying the current and a loose connection is a mechanical failure.

Originally Posted by rdawes

As a HI, I don't know which situation is present.

Then you should opt to start a trouble shooting business as I for one would hire you just to check my circuits for loose connections as you know which situation is present.

Originally Posted by rdawes

So I opt to be safe for my client and recommend that at a minimum that the backstabbed outlet in question be hooked up to the screws.

Why would you recommend something that is tested for the application be changed?

Originally Posted by rdawes

10 years ago my wife was vacuming and said '"there's smoke coming from the outlet the vacumn is plugged into." It was a backstabbed outlet with a bad connection and very hot. The vacumn pulled about 10 amps. Excessive voltage drop can be a hazard. Not all the time certainly but once is enough.

Here the problem was not a voltage drop as you are testing for with your 12 amp load. What you had was a failed connection and is far from being a voltage drop problem.

But then again I agree with Marc;

Originally Posted by Marc D. Shunk

Bottom line... voltage drop causes no problems in a dwelling. The SureTest is an interesting gadget, so feel free to report it's findings. It keeps me certainly employed, and makes me money. Just don't take it too hard when I report back with my professional opinion that no problem exists.

[Robert J. OConnor]

Tripped breakers from things like power tools, hair dryers, and appliances is just confirmation that loads on typical household circuits can indeed reach 15A or more. And what about window AC units, that draw a lot and often run overnight (and have intermittent load surges when the compressor kicks on).

The issue is what if there is say a bad connection on a 15A circuit that is loaded to 15A. That is typically not enough load to trip the breaker. But if there is a loose connection on that circuit somewhere it could initiate a fire that is not immediately apparent, or even further degrade a loose connection to the point where over time normal loads could initiate a fire.

Home electrical fires from things like loose connections is a real risk. If you don't believe me check the NFPA site for more info.

[Robert J. OConnor]

Originally Posted by Mike Whitt

I would recommend using something like this and if it lights up correctly move on to the next device

.

That is generally what I do also. But some inspectors go beyond the standards/minimums and use higher end tools/equipment like a "circuit analyzer". There are positives and negatives to both approaches.

JMO

[rdawes]

Mike,

For anyone who gives a darn about it, here is a link to a better explaination of the formula you posted http://members.aol.com/ocsee/el_calc.htm. That allows you to calculate the VD in the WIRE.

If you read my previous comment, you will see that I said if the 18% voltage drop was distributed in a long wire run that there would be no safety hazard. There is even a formula to calculate how much that wire will heat up. The insulation on the wiring is designed with a large safety factor so that a 15 amp load will never bother a #14 wire in good condition.

Again, if the VD and the energy from it is concentrated in one point then it's another deal. Since a poor connection can usually be considered purely resistive in nature we can use simple formulas the same as if we were dealing with DC. i.e. Power = current X voltage drop. 15 amps x (120 volts X 18%) = 324 watts. In reality, not all of the 324 watts will be in the poor connection since part of it will indeed be in the wire, depending on it's length.

In my case 10 years ago, it was indeed a failed connection that caused a large voltage drop at the outlet which led to heat and then a bit of smoke. If my wife had not noticed it then fire may or may not have followed.

If you or any electrician wants to shrug off a 18% voltage drop at an outlet as no problem, just put it in writing on your company letterhead and sign it. Odds are high that the wrong set of circumstances will never develop to cause a problem and you and the homeowner are both fine and dandy. But if it by small chance it does turn out to be a big deal, the homeowner can then discuss it with you.