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Discussion Starter #1
I have an antique house with some BX wiring probably from the 30's or 40's in addition to Romex circuits. I'd like to plug a small (6000 btu) a/c into an existing outlet on one of the BX circuits but wonder if it can be done safely. The circuit in question only has several outlets with lamps plugged in. The two year old electrical panel is 100 amps. The a/c I'm considering uses 5.3 amps.
Is there a way to determine if the existing 15 amp wiring can safely handle an a/c?

Thanks
 

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If unsure, you can have an electrician come in and do a once over (tighten outlet screws, check to make sure circuit has proper breaker or fuse), and breaker/fuse panel screws are tight, and not loose. You can also do the same, since most is just visual, just make sure power is off on the circuit that you are working on. If you are not the only person in the home, make sure everyone else knows that you are working on the circuit. To find out the total load on that circuit, find out how many outlets, and the devices that are connected to it, and add up wattage as stated on the nameplate for the device, or manufacturer specifications in the instruction manual.

As for the window a/c, it is more of what is called the in-rush current or start-up current that matters, but also keep in mind, long continual running also heats up the junction points, and that can cause problems if wire nuts, or outlet & breaker screws are loose.
 

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Amp wise the circuit can cope with the a/c unit,
Provided the circuit is in good condition,
And there are no other large loads on the same circuit.
But considering the age of the instal,
It would be wise to check it.
Look for loose connections,
Cables in good condition.
GFCI's are also useful if the instal is old.
Consider instaling one.
 

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Discussion Starter #4
Amp wise the circuit can cope with the a/c unit,
Provided the circuit is in good condition,
And there are no other large loads on the same circuit.
But considering the age of the instal,
It would be wise to check it.
Look for loose connections,
Cables in good condition.
GFCI's are also useful if the instal is old.
Consider instaling one.

Thanks for your response. My main question is how do I determine if the circuit is in good condition? I can check each of the outlets on the circuit and verify that the load is not excessive but I can't check the wiring since it's inaccessible.
Re: installing a GFCI, I thought they protected against a fault in the appliance which was plugged into the outlet. Can they protect against a problem (i.e. fault) in the wiring?
If so, will adding a GFCI to the outlet used by the a/c solve my problem?
 

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Discussion Starter #5
If unsure, you can have an electrician come in and do a once over (tighten outlet screws, check to make sure circuit has proper breaker or fuse), and breaker/fuse panel screws are tight, and not loose. You can also do the same, since most is just visual, just make sure power is off on the circuit that you are working on. If you are not the only person in the home, make sure everyone else knows that you are working on the circuit. To find out the total load on that circuit, find out how many outlets, and the devices that are connected to it, and add up wattage as stated on the nameplate for the device, or manufacturer specifications in the instruction manual.

As for the window a/c, it is more of what is called the in-rush current or start-up current that matters, but also keep in mind, long continual running also heats up the junction points, and that can cause problems if wire nuts, or outlet & breaker screws are loose.
Thanks.
If the screws are tight and the breaker is proper (it's 15 amp and 2 years old) and the load on the circuit with the a/c's amperage is no more than 12 amps does that mean I can assume the wire inside the armored cable is OK? Is there any test that can be run to check it? Sort of a stress test?
 

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Thanks for your response. My main question is how do I determine if the circuit is in good condition? I can check each of the outlets on the circuit and verify that the load is not excessive but I can't check the wiring since it's inaccessible.
Re: installing a GFCI, I thought they protected against a fault in the appliance which was plugged into the outlet. Can they protect against a problem (i.e. fault) in the wiring? If so, will adding a GFCI to the outlet used by the a/c solve my problem?
For the highest level of protection instal the gfci at the main panel,
This way all of the wiring is protected.
Installing a recepticule style GFCI,
will only protect the appliance,
and the outlets after that,
which are on the same circuit.
but it will not protect the wiring between the panel and the first outlet,
 

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Thanks.
If the screws are tight and the breaker is proper (it's 15 amp and 2 years old) and the load on the circuit with the a/c's amperage is no more than 12 amps does that mean I can assume the wire inside the armored cable is OK? Is there any test that can be run to check it? Sort of a stress test?
Plugging it in and seeing what happens. Of course, I'm assuming this is a modern, well maintained A/C. I wouldn't go plugging some 15 year old monster with a bad plug into the circuit.

Just don't be foolish about it. Monitor it's use. Don't run it when you are not home. Don't run anything else on the circuit. Make sure you have updated insurance. Check your smoke detectors/change their batteries.
 

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Plugging it in and seeing what happens. Of course, I'm assuming this is a modern, well maintained A/C. I wouldn't go plugging some 15 year old monster with a bad plug into the circuit.

Just don't be foolish about it. Monitor it's use. Don't run it when you are not home. Don't run anything else on the circuit. Make sure you have updated insurance. Check your smoke detectors/change their batteries.
To test the cable, you need to-
Disconnect both ends and measure with an ohm meter,
the reading should be very low,
Now measure between the hot and neutral- should be very high,
Now measure between hot and earth - should be very high.
Measure between the armour if its metal,
and the hot- should be very high.

This is the best you can do with general type servicing tools,
Electricains would use a high voltage tester like a meggar meter.
But handy men dont usually have these specialist type testers.
 

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Measure the voltage out at the air conditioner when it is turned on. The change in voltage should not be more than a few volts and then it is okay as far as the layman can determine.

With a plastic cover over the outlet box it is quite safe to pull the plug out slightly and insert the meter probes between the plug and the receptacle to touch the prongs and measure voltage.

When measuring continuity or ohms, always turn the power off and also disconnect at least one of the wires being tested from any screw or terminal or disconnect all the wires from at least one of the screws or terminals being tested.
 
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