A recent discussion on a German forum prompted me to update my knowledge on US wiring practices and the NEC. Can you tell me what the requirements for the inspection and initial testing for new wiring in domestic and small commercial buildings are (I'm aware that they'll likely differ across states but I assume there's a general basis in the NEC)?
To give you an idea what I'm talking about: most European wiring regulations seem to require visual inspection and beyond that a series of tests and measurements - typically dead-testing insulation resistance at 500 V DC and continuity of all earth and bonding conductors at at least 3 A test current as well as impedance of all earth electrodes and then live-testing loop impedance (i.e. measuring the voltage between all live and earth conductors both without load and under a 10 A load and calculating the impedance from the voltage drop) and trip time and current of any earth-leakage protection devices (GFCIs). Further tests may be required for special systems (e.g. ring continuity in the UK and other countries that use ring mains).
Are there any similar requirements in the US or are you satisfied with visual inspection and checking the correct wiring (polarity) of outlets?
The debate came up regarding the appearance of AFCIs in Germany and the absolute lack of appropriate test equipment for those devices.
I do not know of anything beyond a visual inspection for a normal permit. I did do some impedance testing on one project but this was a special case where we were evaluating the existing conduits to verify they were sufficient for hospital circuits. (redundant grounding). I have also seen guys checking the torque on lugs but that is rare.
As to residential, usual inspections are "Rough Wiring", service, and final. Rough is a visual, for required outlet spacing, circuitry, smoke detectors, etc. Service is riser, meter, panel(s) and grounding/bonding. Final is....'Final'.
Comm is basically the same, with 'above ceiling' thrown in.
Funny, Greg said "checking torque is rare". We do it mandatory on all terminations, from 120/208 to 13.2KV.
Just curious having come from an industry that did random torque verifications during inspections. If you're using the contractor's tools to verify torque, do you verify that the contractor's tools are calibrated properly?
That's quite different - in most European countries the contractors are supposed to do all the tests I listed and document the results including the type, serial number and calibration date of the tester that was used. The relevant tests are supposed to be carried out even after minimal changes to existing wiring, e.g. adding a single socket in a home. Commercial and industrial properties are required to be re-tested at regular intervals ranging from six months to five years depending on risk assessment. In that case portable appliances, extension leads etc. are included (visual inspection, earth continuity, earth leakage mainly). Some companies have banned employees from bringing their own electrical gadgets to work because they're untested and I've even heard discussions about hotel guests bringing their phone chargers and hair dryers etc.