Light Fixture Grounding

Some electrical codes do allow for the use of the cable armour as the circuit protective conductor, but it's generally limited by provisos such as earth fault current carrying ability etc. A separate earthing conductor is usually a better choice, however, if you employ double insulated cable from the junction box to the luminaire, and carry that double insulation all the way into the lampholder, then earthing of the fitting can be foregone. Obviously the above does not apply to luminaires that have other exposed metal that may become live such as ballasts etc.

I'd call an electrician who knows the codes where you are and has experience with old houses.

If you are going to do this yourself you might make yourself very unhappy if something happens. Don't do it!

Usually lights only have 2 wire supply. They are on a different circuit than the power points. If you need ground you will have to pull a new cable there and connect to the poweer points circuit. And thats where you should better talk to an electrician or hire him straight away to spare you the pain. My take is that if the housing is not grounded properly and its wet and the housing gets live all sorts of things can happen.

Good luck!

Good Answer.

A local Electrician will know the pertinent codes for that region and will be able to do the job correctly and safely.

(In Chicago, we allow grounding to the box, because all wiring has to be inside metal conduit, and all boxes must be metal, so the conduit provides an uninterrupted connection to the fuse box/breaker panel, where the panel's ground is bonded to the cold water supply for the house, said piping running straight into the earth serves as a HUGE ground conductor. Remember, for most circuits, the protective ground is there to insure that any break in a 'hot' wire will immediately cause a short and blow fuses/trip breakers, instead of continuing to spark to ground and potentially cause fires.)

What you propose is safe.

While it may, or may not, meet the latest electrical codes, such as NFPA-70, it is safe.

I would not hesitate to do as you suggest.

Let there be light!

Is there metal conduit running from the box back to the breaker panel?

Although I am not quite 135 years old, there was a time when the conduit (if metal) was an acceptable ground path.

Otherwise, if there is NO chance of moisture intrusion into this box, I'd (reluctantly) go with 2 wire.

Any new work should be up to code...the lighting fixture should be grounded to the conduit and the separate ground should feed back to the panel....they can be combined....but you want any short in the light to feed back to the panel ground to avoid shock....

You have not given your location. No one on CR4 can look at the right electrical code.

Other codes may apply - if you are in the UK, the Building Code says that [if you are not a registered electrician], in a residence, a person can only do electrical limited electrical work without notifying the local authority.

This limited work includes adding an outside light connected to an existing circuit, which is your case at worst.

But non-notifiable work is required to comply with the IET Wiring Regulations BS7671 latest issue, currently 2008 amendment 3, 2015: including the required inspection and testing and issue of a minor works certificate.

Having noted that, many lighting fittings are "double insulated" and do not require an earth. These should carry a "two squares, one inside the other" symbol such as appears on mobile phone chargers which do not have an earth pin on the plug or have a plastic earth pin.

Current regulations require an earth terminal to be installed at each light connection point because the fitting could be made of metal and obviously needs an earth. However, since you are only replacing a lamp and are not adding a new circuit, I do not think you are required to add an earth if your fitting is double insulated.

In my memory, back 60 years & most time since most lamps have hung on a cord out of reach and holders were made out of insulating material anyhow.

Lots of modern fittings that look like ancient metal ones are actually plastic.

I should have added [but it was late!] that your double insulated light fitting should be weatherproof (code IP44 or higher numbers, many are IP65) and connected by a cable with an integral insulating oversheath. I would recommend a round section flexible cord rated for outdoor use.

If your house is 115 years old, I would recommend an inspection and test of the electrical installation by an electrician.

In the UK, the regulations which I noted write that a signed Electrical Installation Condition Report, including test results, "shall be given to the person ordering the work", that is you! The report should advise time before next inspection, when the test results will enable deterioration to identified by comparison with previous reports. If you do not get the report, complain to the electrician's certifying authority (reports have been noted more by the omission than presence).

Due to the age of your house, the armored cable or BX cable that currently in place may or may not be solidly connected to earth and grounded back to the main box source. You can use 2 or 3- wires and apply the double insulated approach of wiring as advised and be safe as long as you also will use an all plastic fixtures from the existing electrical junction box. Run the wires thru a small pvc tube to carry the wires to the outside porch.

Double insulated wired devices is an acceptable practice even in hospitals where electrical safety is of utmost importance against minute electrical shocks! Good luck!

If you have armored cable, the wiring isn't as old as your house, that's for sure. My house is a similar age - 146 years. The thing you need to watch for is what the cable is connected to inside the house. You may be dealing with some old knob and tube as well. It was not uncommon to connect directly to it. Left undisturbed it will last for many more years, but the minute you start to work on it or with it, or any rodents get at it, it will likely become a problem.

Yeah, the knob and tube is long gone for my house, and all the wiring in the attic (which supplies power out to the stoop) is armored. A lot of the house was rewired as recently as 10 years ago.

Good for you. One less thing to put spend your $$ on.

Warning, codes and lawyers will eventually get us all. It may be code where you are that all outside fixtures have to be ground-fault-interrupted circuits. Very expensive. If you call in an electrician, he will be obliged to run a whole new wire to a very expensive gfci breaker in your box. If your box is not rated for a gfci breaker, you will need a new box. If the wiring to your box is not rated for the new code, you will need a new feeder to the box, and on and on.

For a test, connect the hot wire to a light fixture and the white wire from the fixture to the armored cable. If the light works bright and proper, the armor is grounded. If not, your circuit is not grounded. If possible, run a dedicated wire from the fixture to ground and do the test again. If that's not possible, install a fixture that can't be touched by passers-by. If it can't be touched, you are safe from immediate concern of shocking someone. You are still at risk of fire if the fixture shorts out and the fuse or breaker doesn't trip right away.

I'd put it on a GFI.