Q: I have read you harping about electrical defects over the years and the importance of getting an electrical permit and inspection. What has particularly gotten...

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I have read you harping about electrical defects over the years and the importance of getting an electrical permit and inspection. What has particularly gotten my attention is when you have written about electrical work by homeowners who aren’t electricians.

I have added plugs, two lights, an additional breaker and a ceiling fan in my previously unfinished garage and bathroom with no problems.

I hope this doesn’t sound ignorant or argumentative, but if the light or the plug works, isn’t that the ultimate proof of the pudding?

First, let me say that I am not opposed to homeowners doing electrical work. Simple replacement of components where wiring connections can be seen and mimicked are hard to make mistakes with.

However, monkeying with complex circuits can be mystifying even to those with experience.

Electrical work is a cerebral and underappreciated skill. The problem is that most people mean well but don’t realize how far over their heads they can get.

To get an idea of how relatively simple things can get fouled up, let’s look at the scope of work you just described, a few new receptacles, an additional breaker, two new lights and a ceiling fan.

Here are some common questions many homeowners can’t answer — and although the lack of knowledge is dangerous, the resulting mistakes still allow the circuits to work:

• Starting at the head of the circuit with the neutrals and ground wires, was this a main panel or a sub panel?

Neutrals and grounds must be tied together on the main panel but separated (floating) on subpanels. There are very few exceptions. If you make a mistake, the circuit will work, but you are left with an electrocution hazard.

• Were the wire gauge and breaker capacities compatible? Install wiring too small or a breaker too big, and you smoke the circuit. This is as simple as knowing and recognizing that a 20 amp breaker is too big for a 14 gauge wire and so forth.

Fires are more common than electrocution.

• Which breaker was the new circuit connected to? Some breakers you can double up; some are doubled to begin with; others can’t be doubled. Do you have space to add a breaker, or should you replace one with a double (peanut) breaker?

Adding an additional wire to a single connection point (screw) is referred to as a “double tap,” a common homeowner mistake that can cause breakers to trip. Only one wire can be tight to the screw. When one wire gets loose as it expands and contracts, it can cause arcing.

• Is that a 240 volt circuit, or is it a 120 volt multi wire branch circuit with a shared neutral? Don’t mistake one for the other.

• If you encounter aluminum wiring, would you know whether it needs any special treatment in your circuit and how to treat it?

What about knob-and-tube wiring? Aluminum wiring issues can take years to manifest and have resulted in numerous house fires. It expands at different rates than copper. Wiring sizes for given amperages are higher with aluminum wiring. Anti-corrosion pastes and special connections also may be necessary.

• Is that light rated for use above the shower?

• What about that older Romex wiring? Is it rated for 60, 75, or 90 degrees Centigrade? And how does that relate to the new enclosed lights you plan to install?

• Is the panel in your house one that trips the breaker only at thermal overload (no short circuit protection)? Do you need a new panel as a result?

• In wiring the receptacles, was the polarity correct? A good percentage of homeowner-installed outlets are wired backward.

• Did you add protective nail plates in front of wiring that could be punctured by drywall nails or screws?

Did you use cable clamps at the electrical panel to prevent wire chafing or cutting at the rough edges of the box?

• Did you use proper solid blocking and a fan-rated rough-in box for the ceiling fan?

• Did the new work tie into the existing bonding and grounding system correctly?

• Did you consider voltage drops through the length of the circuit with a given gauge of wire?

Darrell Hay is a local home inspector and manages several rental properties. He answers reader questions. Call 206-464-8514 to record your question, or e-mail dhay@seattletimes.com. Sorry, no personal replies. More columns at www.seattletimes.com/columnists.