Old house electrical ground wiring:
This article answers nearly all questions about residential ground wiring & electrical grounding safety in older homes. This article explains the more broad topic of electrical grounding.
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Still, grounding is worth adding to your system because it adds protection against electrical shock. Grounding provides a third path for electricity to travel along, so if there is a leak of any sort, it will flow into the earth rather than into the body of a person who touches a defective fixture, appliance, or tool.
[Click to enlarge any image] Sketch at page top courtesy of Carson Dunlop Associates.
An electrical system is grounded with a grounding rod driven at least 8 feet into the ground outside the house or by connecting to a cold water pipe.
Each individual branch circuit must be grounded as well, either with a separate wire that leads to the neutral bar of the service panel or with metal sheathing that runs without a break from each outlet to the panel. (In theory, electrical outlets can be grounded individually, but this is impractical.)
Often an older building has poor or no working local electrical ground, relying instead on the incoming neutral wire from the electrical service.
Or the building's main electrical ground may have relied on connection to a metal water pipe connected to a well; we've found building ground wires connected to a metal water pipe which used to run out of the building and into earth (possibly a pretty effective ground) but where the metal piping exiting the building had been replaced with a newer plastic water line between the well and the building. In other words the local ground was completely ineffective.
Modern electrical grounding at residential properties requires use of one or more grounding electrodes connected by an un-spliced wire between the electrode and the ground and neutral bus in the main electrical panel.
Bare aluminum electrical ground wires are sometimes found to have corroded entirely through where the wire touched a damp foundation wall. We also find that the ground wire between the electrical panel and a building water pipe or grounding electrode has become separated, loose, spliced, or lost entirely, as shown in our photo.
If your outlets have two slots that are the same size, then they are neither polarized nor grounded. These are non-polarized or un-polarized, un-grounded electrical receptacles. This leaves you with no protection against shocks from defective fixtures or appliances using that outlet. At the very least, you need to install polarized outlets. You cannot and should not install grounded electrical outlets on circuits where no ground path is actually present (such as knob and tube wiring). To provide a grounded outlet where no ground is present is dangerous.
Some locations in your house- especially where the outlet and/or appliances may become wet- require ground-fault circuit-interrupter (GFCI) receptacles. Older, ungrounded circuits usually are protected by polarization, which is less effective than grounding but better than nothing. Grounded and polarized receptacles work only if they are wired correctly.
An older home may have electrical service that is inadequate or even unsafe. It can be confusing, as well. If you are unsure about your home’s wiring, have a professional check it out.
See False Ground at Receptacles for examples of how wiring mistakes on un-grounded or even grounded electrical circuits can be dangerous. That article includes false neutral connection discussion too.
Here are a few things to consider when inspecting the electrical system in an older home.
Warning: this list of electrical wiring defects and safety concerns in older homes is incomplete.
Contact Us to suggest corrections, changes, or to add additional items.
Please see KNOB & TUBE WIRING for a detailed discussion of the identification, inspection, and repair of this electrical wiring system.
Knob and tube electrical of wiring has been installed in homes from the 1920s right up into the 1970's in some jurisdictions.
Knob and tube electrical wiring may be functional in a home and it was in its original concept a safe wiring method, separating the two conductors in air (see our photo at left) and using durable ceramic insulating knobs and tubes to mount the wire.
Knob and tube electrical wiring may not need to be replaced, but it certainly deserves careful inspection and possibly replacement or repair, because knob and tube systems lack an electrical ground (less safe), may have damaged insulation (less safe), or may have been improperly modified or extended (unsafe).
Loose taped wires, old wire damaged because it’s exposed, and multiple wires slipping off a single terminal screw may seem like minor problems, but are not.
See ELECTRICAL CIRCUITS, SHORTS for more about short circuits, how they happen, how they are corrected.
For an example of installing an additional electrical receptacle, see Electrical Outlet-how to add.
"Polarity" in an electrical receptacle and on the device that plugs into or connects to it means that we're making sure that we connect the "hot" or "live" side of the electrical circuit to the connection point in the appliance or device that was intended to be "hot" or "live".
Carson Dunlop's sketches show why it's important to respect polarity when connecting an electrical receptacle, a lamp or any other appliance.
Never clip or file down the prongs on a grounded or polarized plug in order to force it to fit into an older electrical receptacle. The risk is that your plug will be installed with reversed polarity - connecting the "hot" side of the electrical circuit to the normally neutral-wired side of the appliance. We've found appliances (a coffee maker) that simply burned up when connected in this fashion.
Watch out: Safety Warning: Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death.
Even when a hot line switch is off, one terminal on the switch is still connected to the power source. Before doing any work on the switch, the power source must be turned off by setting a circuit breaker to OFF or removing a fuse.
Elizabeth Sluder contributed to the original text of this article.
Watch out: for safety, also review SAFETY HAZARDS & SAFE ELECTRICAL INSPECTION PROCEDURES for Inspectors examining Residential Electrical Systems and Local Electrical Grounding for safety procedures during inspection of the grounding system.
This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions. Critique and content suggestions are invited.
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(Jan 28, 2014) Crank said:
On these pipes I need to put a heat cable to prevent the water pipes from freezing . Can I heat the pipe to 48 degrees with out messing up my grounds.
Sorry I don't understand the question. Certainly the heating cable would not normally interfere whatsoever with the electrical conductivity of metal water piping that itself is grounded.
In fact there will be no electrical contact between pipes and heater cables - that would be a short circuit and should trip a breaker, blow a fuse, and damage the heating cable.
And the change in pipe temperature won't harm its conductivity.
But the question leaves me worried by the phrase "messing up my grounds" - I'm not sure what you are actually considering.
If there is any doubt whether or not the building electrical ground system is complete and proper it would make sense to ask a licensed electrician to review it.
26 Feb 2015 Bob said:
I'm redoing my kitchen, including ALL electrical. I ran a subpanel and ran all the required circuits from there.
My house was built in 1930. Electrical has been upgraded from knob and tube to metal clad without ground wire.
the bathroom upstairs was wired into the kitchen circuit, so now that I'm done with the kitchen there is a 2-wire cable hanging out of the kitchen ceiling and no electrical to the bathroom.
How do I tie the old ungrounded 2-wire metal clad into the new up-to-code grounded system of the kichen? Do I have to tear out all the walls and upgrade the bathroom now?
For un-grounded circuits you need to only install un-grounded receptacles; you don't have a grounding conductor to connect to the rest of the buiding's ground system.
The armored cable will be grounded to the main panel or sub panel, but that's not a ground path for the circuits themselves.
The safer (and more costly) alternative is to re-wire the circuits entirely or to add n approved a grounding conductor throughout the old 2-wire circuits, junction boxes, receptacles, switches, electrical outlets, fixtures, etc.
28 Feb 2015 Bob said:
So, just to clarify:
There are no outlets on the bathroom circuit.
So I can tie the metal clad cable from the ceiling into the new junction box in the kitchen even though it doesn't have a ground?
Bob I'm nervous about this as I don't really know what circuits are going where; if you are permitted to do your own wiring where you live you will still want to follow code and most likely need a permit and inspections, right?
The ceiling armored cable - is powering what? Are you connecting an old circuit to a newer one to extend the old circuit or what? I ask because in some cases you don't want to extend (add stuff to) an existing older circuit; the risk is overloading it, apart from the grounding questions.
Keep in mind that if you're discussing wiring into a bathroom, those circuits need GFCI protection. A GFCI can protect against some electrical faults even if there is no ground but one can't test that it's working properly using the test buttons as those short to ground.
28 Feb 2015 Bob said
Thanks for the reply.
No need to be nervous: I redid the bathroom a few years ago, added recessed lights, 3 GFCI outlets, and exhaust fan. All up to code on their own circuits into the new 200 amp main panel in the basement.
The only thing that existed at the time was the armored cable, non grounded circuit that came up in bathroom floor and went to the light fixture over the sink. I didn't rewire that.
Basement has the main panel, 1st floor is kitchen, and directly above kitchen on 2nd floor is the bathroom.
I'm now redoing the kitchen. I tore out all the non-grounded armored cable in the kitchen. The entire kitchen was fed by 1 armored cable from the basement on ONE circuit breaker, with lights and outlets on that 1 circuit. The armored cable that goes upstairs to the bathroom light fixture ALSO branched off from that kitchen wiring.
I've put a sub-panel in the kitchen and all wiring is up to code including 2 separate 20amp GFCI outlet circuits for the counter top spaces, dedicated 20 amp circuit for the dishwasher. The kitchen now has 6 total circuits for lights, outlets, etc, all grounded w 12/2 and 14/2 NM romex.
The problem is that single ungrounded AC line hanging out of the ceiling that goes upstairs to the light fixture in the bathroom. Because it is no longer tied into the kitchen wiring, the light fixture is dead. How do I deal with it? can I tie it into the metal light fixture box in the kitchen, even though it doesn't have a ground, or do I have to tear my bathroom apart and run 14/2 romex grounded all the way to the main panel in the basement on it's own circuit breaker???
I am doing the work myself. A check with City Hall assured me that I can do the work and have it inspected afterward as I did when I upgraded my FUSE box (with a total of 4 fuses!!) to 200 amp main panel with 40 spaces for circuit breakers.
I didn't see an a question in your last longer comment that could safely be answered with no knowledge of the building and it's wiring, and we don't want to reply with mere arm-waving.
In general terms, all of the circuits in a modern home AND circuits that you work on in an older home should meet current electrical codes, including the provision of a grounding conductor and proper ground bonding in the junctiong boxes and connections to receptacles and light fixtures.
Certainly some light fixtures don't include a ground connection but many do, as a small copper wire coming out of the fixture base.
Bathrooms are areas of extra shock risk for obvious reasons: wet, proximity to plumbing. That's why GFCIs are required on receptacles there - your bath has omitted receptcles. You might consider the location of the light fixture. For example if it's conceivable that someone could touch the fixture and a sink or tub or pipe or wet surface the risks are increased and you'd perhaps be encouraged to add GFCI even on the lighting circuit. And grounding.
The "Code" question for your renovation work, in final authority, is in the hands of the local electrical inspector whose word is law. So if your question meant to ask "am I allowed to do x" it'd make sense to ask ahead of time directly the fellows who might otherwise make you do the work over again.
Ultimately and subject to inspection, you will decide if you are going to wire to current codes (including electrical grounding) or if you'll do what "works" to give light and take the remaining risks.
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