TL;DR Unless there is a major panel replacement needed, you're looking at hundreds to replace every receptacle and/or add GFCI protection, not thousands.
The electrical code (NEC) and actual practice have evolved over many years. Ungrounded receptacles are not ideal, but are not inherently unsafe. If they were, then there would be no such thing as devices that use two-prong plugs instead of three-prong plugs, but plenty such devices are still manufactured - including cell phone chargers, lamps and many small appliances.
In a perfect world, every advance in safety would be retrofitted everywhere. We don't live in a perfect world and we need to balance the cost vs. benefit of such changes. My personal opinion is that the most beneficial change is GFCI - it provides critical life-safety protection at a relative low cost, and despite "ground" in the name, it can be done without a ground wire!
Your specific situation sounds like many houses from the early-to-mid 20th century. There are actually a few possible situations, and you may even have a mixture throughout your house:
Types of Receptacles
- 2-prong receptacles with no ground available
These are quite common, and in areas that don't have a major water concern (living room, bedrooms, etc.) it is OK to leave them as is. But if you want to add some real protection, you could upgrade to GFCI-without-ground (more below).
- 2-prong receptacles with ground available
If you have metal conduit and metal junction boxes, then you may be able to use that as a ground connection and install grounded receptacles easily.
If you have non-metal conduit, you can add a ground wire relatively easily. Just add a bare or green wire of the appropriate size (12 AWG for 20A, 14 AWG for 15A) into the conduit.
You may also have cables that include a ground wire and find that it is available to connect to the receptacles.
In these three cases, you can install grounded receptacles at minimal cost.
- 3-prong properly grounded receptacle, without GFCI
This is likely what you have in the bathroom. If so, upgrading to GFCI protection (more below) is a really good idea.
- 3-prong receptacle without a ground connection.
There is a small possibility you have these receptacles. If so, that is a real hazard as it provides the appearance of protection without actually protecting you. These should be upgraded to GFCI protection.
- 3-prong receptacle with a bootleg ground
This is where ground is connected to neutral. Not so likely here, I hope! But possible if the owner before the last one had a situation of: Home inspector says "you should have grounded receptacles in the bathrooms", owner "fixes" by replacing 2-prong receptacles with 3-prong receptacles but wires neutral to ground instead of running a new cable with a ground wire, buyer tests (but doesn't open receptacles) and verifies that all lights on the tester are "good". The only way to tell if you have a problem of this type, which would be a big red flag about workmanship throughout the house, is to open up a receptacle and see how it is connected. But even if you find such a mess, it can be resolved by putting in a GFCI and leaving ground disconnected.
Add a Ground
It is now legal under the NEC to add a ground wire without actually replacing existing wiring. You can:
- Run a ground wire (bare or green) to an already protected circuit
- Run a ground wire next to your cable, all the way back to the panel
- Run a ground wire through any convenient path, all the way back to the panel.
Any ground wire must be the correct size (12 AWG for 20A, 14 AWG for 15A) but can always be larger. The full path must be the correct size - e.g., you can add a 14 AWG ground for a 15A circuit into an existing 12 AWG ground for a 20A circuit, but not the other way around.
Fuses and Breakers
You may fuses, circuit breakers or a combination. If you have circuit breakers then you may be able to retrofit GFCI protection by replacing breakers. However, many older panels do not have GFCI breakers available.
Some breaker panels are BIG problems. I would be much more concerned about the status of the panel than grounding of receptacles. Federal Pacific is one that comes to mind, and I think there are others. Plus even a good panel can have improper wiring, wrong breaker types or other problems. Upload a picture of your panel and the experts can give some advice.
GFCI, Ground Fault Circuit Interrupters, watch for any imbalance in the current going in/out of the circuit, either between two hots (240V) or between hot & neutral (120V). Any "lost" current is considered a ground fault, but that doesn't mean it went through the "ground wire", it could be going through a person to the physical ground, which can be deadly. A GFCI acts fast enough to save lives. Areas with water are the most vulnerable, since wet skin conducts much better than dry skin. As a result, GFCI protection is, generally speaking, require in new circuits in kitchens, bathrooms, laundry rooms, garages and outdoor receptacles.
The good news is that GFCI protection (a) does not actually need a ground wire to do its job and (b) can be installed wherever it is easiest - in the breaker panel, between the panel and the first receptacle to be protected, or in combination with the first receptacle to be protected. If there are multiple receptacles on one circuit to be protected, they can all be protected with one GFCI unit, provided it is properly installed.
The end result is: If you are concerned about lack of grounds, and there are no ground wires available, you can protect the circuits using GFCI at a reasonable cost.
However, while GFCI-without-ground-wire does provide life-safety protection and also effectively takes care of certain other faults that would not in the general sense, in the absence of wet skin, be considered immediate life-safety threats, that would otherwise get handled by the traditional ground wire, it does not take provide a route for the energy that surge protectors would normally dump on the ground wire. If you have sensitive electronics designed for a 3-prong connection, they (and any surge protectors they are plugged into if they are not plugged into a receptacle directly) ideally should be connected to actual grounded receptacles and not receptacles that have GFCI-without-ground-wire.
You can get a simple tester like this one:
to test receptacles to see if they are properly grounded (and check for certain other problems as well) and also to see if they are GFCI protected. Note that, ironically, the GFCI testers often do not work if there is no ground wire, because they work by taking some of the current that should be going from hot to neutral and sending it to ground. If there is no ground, then the current doesn't flow - and the GFCI doesn't trip!