Electric wiring question in a new old house
May 29, 2016 5:30 PM   Subscribe

I am in the process of buying a new (to me) old (1942) house. Hooray! I just had the inspection done and have some questions about the wiring. I'm planning on hiring an electrician, but want to have an idea of what I might be getting myself into as well as safety concerns...

The inspector said the breaker box looked old but good, and noted there's no earth ground to the outside. Inside the house about half of the plugs are 2 prong, the others are 3 prong. In the kitchen they are GFCI, and not tagged as "no equipment ground". There appears to be one circuit (three 2-pronged plugs in a row) that were noted to have reversed polarity. I asked the inspector and he said I should have an electrician come out and put in an earth ground and fix the reversed circuit. Fair enough - electricity scares the bejesus out of me and I have every intention of hiring a professional; yes even for something "easy" like swapping out an outlet. Here are my questions:

Does the lack of an earth ground mean that there's no ground to the house?

If that's the case, then how are there grounded plugs installed at all?

The appliances are all new - surely they need a ground to work properly, right?

How difficult is it to fix that one circuit with reversed polarity?

I apologize in advance if these are stupid questions. I've been reading nonstop since the inspection, and while I've easily learned about and am comfortable with the idea of - say - how to remove, strip and reglaze a window, electrical systems remain DANGEROUS WIZARDRY in my mind and I can't seem to wrap my brain around it.
posted by lilnublet to Home & Garden (17 answers total)
 
In general, your wiring is BETTER than I would expect in a 1942 house, so the panel was likely upgraded at some point. As the inspector said, get a real ground installed, and fix the reverse polarity on that one circuit. None of that is particularly complicated, so go ahead and do it. But then quit fretting about it and move on.
posted by intermod at 5:45 PM on May 29, 2016 [1 favorite]


Does the lack of an earth ground mean that there's no ground to the house?
Yes, that's probably it.

If that's the case, then how are there grounded plugs installed at all?
They're not really grounded or they're grounded to somewhere else other than the main box - depending how they're grounded this is either no big deal or an accident waiting to happen.

The appliances are all new - surely they need a ground to work properly, right?
Appliances don't need a ground to operate under normal conditions - only if there's a short inside the appliance does the ground come into play.

How difficult is it to fix that one circuit with reversed polarity?
Quite simple.
posted by GuyZero at 5:53 PM on May 29, 2016


Yes, that doesn't actually sound like a bad electrical report for a 1942 house.

If the house still has old "knob and tube" wiring that's going to be a problem -- not only is it not safe but you might have difficulty finding an insurer who wants to deal with it -- but the problems that you've mentioned are ones which can be relatively easily remedied.
posted by Nerd of the North at 5:55 PM on May 29, 2016 [1 favorite]


You can buy a receptacle tester for $5.00 at any hardware store that will tell you if the 3-prong outlets are correctly grounded and have the right polarity.
posted by octothorpe at 5:56 PM on May 29, 2016 [3 favorites]


Not to thread-sit, but no earth ground means there's no ground for the whole house, not just that there's no ground to the panel? And even though that sounds worrisome, it may not actually be a big deal?
posted by lilnublet at 6:01 PM on May 29, 2016


Unfortunately for octothorpe's suggestion, I have two $5 electrical testers, and at least one of them requires very little ground to register as a ground. Like 50' of 12ga wire unconnected at the other end will register as a ground. The testers are great, but they're unlikely to tell you if the ground in these sockets is hooked up correctly.

I'm gonna guess that these ground wires are hooked to your water pipes, which is either good (you have metal from where they are hooked to your water pipes, and then into the ground) or bad (you have plastic where the service goes into the ground, so it's an electrocution hazard waiting to happen).

It's more likely good.

But/and: The ground is there as a safety measure. Yeah, if things go bad it could be bad, but for the types of issues that modern electrical code is accounting for, you're still way more at risk driving to work than this. Fix it, fix it expeditiously, but don't loose sleep over it.
posted by straw at 6:10 PM on May 29, 2016 [1 favorite]


In every household breaker box I've ever opened up, ground and neutral are connected together, at the same bus bar. The presence of a separate ground conductor in the cables and equipment facilitates a number of protection schemes but they are ultimately connected together at the box.

In many systems "earth ground" is provided by connecting to the water pipes, frequently with a clamp and big braided wire going back to the distribution panel. This works fine assuming your original metal water main hasn't been replaced with PVC, which sometimes happens. If for whatever reason your pipes are not reliably electrically connected to the ground, they'll install a long metal spike into the ground to serve as an explicit earth ground reference.

My understanding is that you want a local earth ground so that the voltages in your house, most importantly ZERO volts, are relative to the house itself. Without a local earth ground your neutral can drift some, resulting in weird behaviors. I'd guess that in most installations your neighbor's earth grounds do a pretty good job of tying you to local ground but it's probably not a great idea to count on that forever. Your local power company may well care even more about this than you do, so don't be shy about asking them directly.

(For example, in my old lab at MIT I once pulled a beautiful 2" blue spark between two alleged ground conductors. Eventually we figured out that one of the two branch circuits was locally grounded, the other grounded about a half mile away...)
posted by range at 6:23 PM on May 29, 2016 [1 favorite]


If the house still has old "knob and tube" wiring that's going to be a problem -- not only is it not safe but you might have difficulty finding an insurer who wants to deal with it -- but the problems that you've mentioned are ones which can be relatively easily remedied.

The front of our home had "knob and tube" wiring and, while we had no grounded outlets in that part of the house until I updated it, and while this could be local to state and city code standards, there was no issue with insurance. Existing knob-and-tube is generally considered safe, although any new electrical permits would certainly call for work that puts in grounded lines to feed tamper-resistant ("child-safe") outlets.

If you're concerned, you can test the three-prong outlets with a $2 tester available from your local hardware store. The tester has three lights on it that either light red or green. Depending on the pattern, you either have a grounded outlet or something else (not grounded).

Ideally, you want grounded outlets for modern wiring, and GFCI outlets in kitchen and bathrooms (or similar locations where there is added risk for accidental electrocution).
posted by a lungful of dragon at 6:27 PM on May 29, 2016


IANAE, but I've had to deal with a variety of electrical situations on the job.

Does the lack of an earth ground mean that there's no ground to the house?

Nnnnnnot necessarily? But an actual electrician would need to inspect in person to really tell you. Ground and neutral may be connected together inside your breaker box. It used to be legal (dunno if it still is) to ground via the cold water pipes, or if your wiring is inside metal conduit the conduit itself might be tied to ground somewhere, or at the least I believe there will be a ground connection at the pole and/or transformer near your house. Some/all of your outlets may be grounded, buy the tester octothorpe suggests. (This thing.)

Grounding is essentially a safety issue, so things that used to be "acceptable" for grounding are no longer up to modern code or approved by inspectors. A ground directly out of your main breaker box is the current way to go, but the lack of that direct wire is not necessarily a sign that the whole house and all outlets are ungrounded.

then how are there grounded plugs installed at all?

You just don't connect the non-existent ground wire. Which is to say it's entirely possible that a 3-prong outlet is actually un-grounded.

In the kitchen they are GFCI, and not tagged as "no equipment ground".

There is a way to install a GFCI outlet that essentially bypasses the GFCI part, so it could be just wired as a regular outlet.

The appliances are all new - surely they need a ground to work properly, right?

Nope. As above, grounding is about safety, the electricity still flows through the positive and negative connections regardless of ground.

How difficult is it to fix that one circuit with reversed polarity?

Probably not tough at all - most likely the wires got put into the opposite terminals at the first outlet, so then the next plugs in line are also backwards. But while you've got an electrician digging around, you might as well have him install 3-prong outlets, if he can ground them properly.

Pic of a receptacle, front and back.
posted by soundguy99 at 6:29 PM on May 29, 2016


lilnublet: "Does the lack of an earth ground mean that there's no ground to the house?

Maybe. The ground may have been picked up at water pipe or other source away from the breaker box for the grounded receptacles.

If that's the case, then how are there grounded plugs installed at all?

See above. Or just as likely someone just replaced the ungrounded outlets without actually grounding the receptacles. Also a single GFCI outlet can protect any 3 prong receptacles down stream.

The appliances are all new - surely they need a ground to work properly, right?

For the most part no; the ground is mostly a safety feature rather than a operational requirement. Some electronics can behave badly if connected to an ungrounded outlet but it is rare.

How difficult is it to fix that one circuit with reversed polarity?
"

It's just a matter of swapping two wires but it may take a while to find where the wires are incorrectly connected depending on how logically the circuit is laid out.

Nerd of the North: "not only is it not safe but you might have difficulty finding an insurer who wants to deal with it"

There is nothing particularly wrong with knob and tube wiring if it hasn't been hacked up by a "handyman". However the age of of it makes that likely which is why insurance companies don't like it. Also 1942 is pretty late to have knob and tube; not impossible but at the time it would have been cheaper to use other wiring methods.

octothorpe: "You can buy a receptacle tester for $5.00 at any hardware store that will tell you if the 3-prong outlets are correctly grounded and have the right polarity."

You can't trust those devices to tell you if a recpetacle has been intentionally wired incorrectly to provide a fake ground. Physical inspection is required.

Re: magnitude of lacking ground. straw right, this isn't anything to particularly worry about short term. Your house isn't in any danger of imminent fire or anything (or at least no more than any other 50+ year old residence with unknown electrical maintenance quality). But getting your system updated including replacing all receptacles would be a statically significant increase in safety.
posted by Mitheral at 6:32 PM on May 29, 2016 [1 favorite]


range: "My understanding is that you want a local earth ground so that the voltages in your house, most importantly ZERO volts, are relative to the house itself."

No. The requirement to bond your neutral to ground is to provide an alternate return path for current if a short occurs to bonded metal. Without the ground a short won't necessarily trip the breaker.

soundguy99: "There is a way to install a GFCI outlet that essentially bypasses the GFCI part, so it could be just wired as a regular outlet. "

I don't know if this was true at some time in the past but it's not true for modern devices.

PS: lilnublet your electrician might find your boxes are too small to fit GFCI receptacles and will therefor have to use more expensive remediation methods (replace boxes, add additional outlets, use GFCI breakers etc.).
posted by Mitheral at 6:40 PM on May 29, 2016 [1 favorite]


For your purposes, you can think of the electricity as arriving at your house on one wire, then going through your appliance to do whatever the appliance does, and leaving on a second wire. The fact that it's AC (alternating current) means that the electricity goes both directions, but you can think of it as being pushed or pulled via one wire, and the second wire just lets enough in or out to match the push or pull.

So that's why two-prong plugs work: you just need "in" and "out," or "push/pull" and "thing that's being pushed or pulled." (In contractor terms, those are called "hot" and "neutral.")

Most appliances don't really care which side of the plug is actively being pushed or pulled, and which side is passive, but there's some safety benefits from having the same sides being used everywhere, which is why modern plugs often only fit one way -- the "hot" or "push/pull" side is the narrow prong, and the "neutral" or passive side is wider.

Ground is another thing entirely: it can act like neutral (you can push to or pull from it at will) but it's supposed to be connected to the outside metal case of things. The idea is, if any electricity gets loose inside the case, it shouldn't have to go any further than the case and then back via the ground (instead of going back through your finger, arm, heart, foot, and shower drain!) In most construction, ground and neutral are hooked together at the panel where power arrives at your house. And GFCI plugs detect if any electricity flows in the ground circuit (where it shouldn't be). If you have a ground problem, the plug breaker shuts everything down.

Does the lack of an earth ground mean that there's no ground to the house?

Maybe, maybe not. Ground is usually connected to neutral at the panel, and there's a wire from there to an actual copper stake in the ground nearby. Sometimes they'll connect to a water pipe instead, because it's copper and buried in the dirt.

If that's the case, then how are there grounded plugs installed at all?

They might be unconnected, or connected to neutral at the plug, or connected to a water pipe somewhere nearby.

The appliances are all new - surely they need a ground to work properly, right?

Very few things need a ground to work properly. They're safer with it, but they'll work without it.

How difficult is it to fix that one circuit with reversed polarity?

Easy-peasy. But have an electrician do it if you don't know how.
posted by spacewrench at 6:47 PM on May 29, 2016


Mitheral: No. The requirement to bond your neutral to ground is to provide an alternate return path for current if a short occurs to bonded metal. Without the ground a short won't necessarily trip the breaker.

Just to make clear to the OP that there's less disagreement than it seems: I totally agree with the above (and tried to allude to it in a different part of my answer but apparently failed to be clear).

Electrical nerdery to follow: What's not super-obvious to me is how important it is to have your house ground wiring tied directly to the dirt your house is standing on. In the absence of that connection (via pipes or a spike), most houses would have a combined ground/neutral at the box that would be tied (a) as a return to the transformer on the pole and whatever earth-ground connections might be there and (b) to the earth grounds provided by other houses on the same neutral run from the transformer. I'm curious if anyone else knows the design logic behind this piece of the infrastructure, as at least around here the power company isn't in a big hurry to put in a ground spike when your water main is converted to plastic.
posted by range at 7:09 PM on May 29, 2016


I've been taught it's important enough that I'm surprised the power company doesn't care.

Residential wiring nerdery: It's important that all the non current carrying metal in a home be bonded (connected) together because otherwise two pieces of metal could be at different potentials (for REASONS!) and if you were to touch both pieces at the same time you could get a potentially fatal shock. Since some of the metal is potentially already touching the earth (water lines, gas lines, underground electrical conduit, metal siding, rebar in concrete etc.) we make an intentional connection to ground to make that the default potential. This would all work even if the neutral was not bonded to ground in your panel (IE: bonding would work even if the white neutral wire was not connected to the rod driven into the ground).

However without the neutral connected to the ground wire at some point (we select the panel for other REASONS!) a short to ground in your electrical system may not have a sufficiently low impedance return path that would trip a breaker. In fact in a perfectly setup up system without a neutral bond (which is done in some special industrial cases) a single short to ground doesn't trip a breaker even if you have dozens of amps and hundreds of volts available on equipment. Those systems are monitored in other ways to detect ground faults.

PS: there are numerous ways to pickup a system ground so lack of a ground rod doesn't necessarily mean the system is ungrounded.
posted by Mitheral at 7:37 PM on May 29, 2016


For complicated reasons not worth explaining here, it's most likely that even if your house doesn't have an earth ground at all, the neutral wire connected to your house will be grounded at the pole that supplies you. There are scenarios in which that could cause a problem for you, but they are really uncommon.

I'd still want to get it fixed, because there are lots of ways that using pipes as ground can go wrong. If the supply line has been replaced with something nonconductive, as mentioned above, that could cause some shocking incidents. But also, using pipes as ground can cause the pipes to galvanize, which can lead to really expensive problems.
posted by fedward at 9:54 PM on May 29, 2016


then how are there grounded plugs installed at all?

It's pretty common for people to replace two-prong receptacles with three-prong, just so their newer appliances can be plugged-in.
posted by Thorzdad at 7:42 AM on May 30, 2016 [1 favorite]


it's funny you post this now, since I've been reading Shapiro's excellent Your Old Wiring this weekend for fun (don't mock me). Most of this stuff is mentioned in there as pretty common and pretty easy to fix. As long as nobody is ALREADY getting shocked by some appliances, you are not in any imminent danger.

An answer to a question you didn't ask: old switchboxes can be just fine, but it is also not uncommon for there to be no more replacement parts made. if you're considering getting any new circuits put in, it may be necessary to replace the switchbox, in that case. it's worth asking your electrician about that, just so there's no more unpleasant surprises in future.
posted by ivan ivanych samovar at 11:25 AM on May 31, 2016


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