I just received a set of plans with the following specifications:
-"At the time of the final electrical close out, and in the presence of the general contractor, architect, or owner, the electrician shall apply a minimum load of 3 amps to the distal end of each electrical circuit. The home shall be inspected under load using a gauss meter. Any elevated magnetic fields greater than .5 miligauss will indicate the presense of a code violation or that wiring has been damaged during the construction."
I'm not sure how that indicates a code violation or damage to wiring, but EMF levels above 4mG are suspected to cause leukemia.
You'd measure it by walking around the house with a probe. Strongest levels would be near the wiring.
I suppose it could indicate that you have leakage current or a multigrounded neutral, as the currenet in the hot conductors and neutral will always be opposite and the subsequent magnetic fields almost perfectly cancel each other out... Just don't use a hairdryer as your load- they put out something like 300 milligauss at 6'!
Re: "green house" bid#75844 03/14/0707:12 AM03/14/0707:12 AM
It could mean nothing, I take lots of contracts with silly crap like that in it and nothing ever comes from it… but there have been a few memorable times when the goofy engineer who wrote that crap showed up to follow through, or even worse some over zealous GC felt like he had to enforce every last letter of the specs when the engineer and owner were happy with the project.
My feeling is, that is this is a “green house” project and there is a real potential that you may have to go through this test should you get the project, then make sure there is enough money in your proposal to cover the headache.
On a side note I was not aware that NEC says this, it sounds like some egg head made it up:
“Any elevated magnetic fields greater than .5 miligauss will indicate the presence of a code violation or that wiring has been damaged during the construction”
101° Rx = + /_\
Re: "green house" bid#75845 03/14/0708:16 AM03/14/0708:16 AM
We see even goofier reqiurements in voice/data cable installations where "consultants" or IT people write the specs. We know that the customer is being sold a bill of goods with gross overkill to address future capacity. These guys have customers spending 3-4 times what the job should really cost by demanding printed test results, 30 year warranty, on and on and on. No customer is going to stay in the same spot for 30 years and even if they did, technology is growing/changing at such a rapid pace that the overkill the customer paid for is obsolete within 7-10 years.
"But the guy at Home Depot said it would work."
Re: "green house" bid#75846 03/14/0711:30 AM03/14/0711:30 AM
I would first say that the specification as written cannot be met.
1) The Earth's magnetic field at the surface is on the order of 300 - 600 milligauss. Kind of blows away the 0.5 milligauss maximum. Of course, the specification should really differentiate DC magnetic fields and AC magnetic fields.
2) Conductors carrying current always create a magnetic field. In a properly wired electrical system, the balanced current flow between adjacent circuit conductors will mean that this magnetic field falls off very quickly. But in the space _between_ the conductors the 0.5 milligauss threshold will be exceeded. There is no specification for the locations to be surveyed, and no exclusion of the wires themselves.
3) There is no differentiation between magnetic flux caused by your wiring and magnetic flux caused by other systems. You don't want to be on the hook for flux caused by current that you don't control. If the flux is present with your circuits off, you shouldn't be on the hook for fixing it.
4) I would want to see a baseline survey as well as a survey after all building steel and grounding electrodes were placed.
5) While you should be on the hook to correct your wiring defects (eg. crossed neutrals, neutral-ground faults, etc) you shouldn't be on the hook to pay for the magnetic survey time to find these defects.
When you quote the job, price it out as you normally would, then itemize each of the silly tests, specifications, and other nonsense, and watch how quickly those items get dropped from the plans. If they don't get dropped, at least you know the client you're dealing with has more dollars than sense.