If the reading was the same as the line to a direct ground
(water pipe or whatever), probably 110 or 120 vac in your case
its legal in most places to use the conduit as the recepticle
*ground.... the green terminal, not the neutral although some
people use the conduit as the neutral because it 'works'... it
is also a severe fire hazard.
Grounding is a significant issue. Especially if electronics
are involved ....how well the driven ground is attached to the
grounded electrical panel and its connected conduit is a
Usually its legal to use the conduit as a ground though you
should ask you local building depts electrical inspector.
The quality of the existing conduit is an issue..if thats
sloppy, corroded or not fully connected etc then its a poor
ground even if it reads as a ground when you check it.
One of the problems is the current carrying capacity of the
conduit ground...it might check ok with a regular ohm meter,
but not with a load applied (meg ohm testing). Most systems
these days run a separate green or bare copper ground wire.
Retrofits can have different rules as long as the local
building authorities agree.
Hmm what don't you understand about:
1) There is an older part of my house that has steel or galvanised pipe for
2)I test the positive against the housing and get a reading,is this an
3)or should I run a wire from the house ground to put a three prong plug
You are an electrician of sorts no? who has to deal with the general public?
Read them one by one and then draw a picture in your mind of a house with
galvanised pipes with electrical wires running through them and someone
wanting to insall a three pronged plug receptacle where one wasn't before,
and wanting to use the housing that is connected to the galvanised pipe
showing that it is grounded by testing the positive cable against it with a
meter as the ground.
So what you're asking is if it's OK to use the conduit as an
equipment ground for the 3 wire outlet?
Checking voltage as you did only proves the connections in the
conduit were good enough to make the meter work. It won't guarantee
that it's a good enough conductor if there is an actual fault condition.
This statement is decidedly 'non-conforming'. Just what do you mean by
'test the positive'?? Do you have a DC installation? Or are you trying to
say you tested with a voltmeter between the 'hot' conductor and the housing
and got something other than zero volts?
Again, there is no 'postive cable'. There is a 'hot' wire and a 'neutral'.
Also referred to as a 'non-grounded current-carrying conductor' and the
'grounded current-carrying conductor'.
From your description, it *sounds* like you tested between the 'hot' and the
housing and got a reading. What kind of reading did you get? If you read
60VAC, then no, you shouldn't try to use the housing as the ground. Even if
you read the same voltage as between hot and neutral, you still might not
want to use the housing as the 'grounding conductor' (note the difference
between 'grounded current-carrying conductor' and 'grounding conductor').
If the various conduit connections and joints between the new receptacle and
the service panel have a variety of resistances that add up to something
like 240 ohms, then your voltmeter reading would still show the same, but it
would be very poor grounding connection. (a direct hot-ground fault would
only draw 0.5 amp, not enough to trip the breaker (unless it's GFCI), but
would raise the frame of any appliance to ~120V)
This is why some areas require separate grounding conductors, regardless of
metal conduit ('pipes'). Or if the conduit *is* used for grounding, special
precautions are taken at the joints to be sure of clean, tight connections
(one of the reasons for those 'funny' locking nuts on threaded fittings is
to maintain good electrical contact).
no you can not use the water pipe as a ground conductor.
Best way is to run a new cable to the service.
Next is to run a ground wire, BUT the ground wire must take the same path as
Even though using the pipe as your ground connection MAY meet the
regulations you are required to follow, and it MAY even be safe to do so
assuming that all the pipe joints make a good enough connection, I would
recomend running your wiring for any new outlets using wire that meets the
current wiring codes as if it were a new installation...... ie:- run new
wires for all 3, active, neutral and earth.
Running new 3 core cable is going to make sure your installation is a safe
as possible, rather than taking a risk.
If you used a solenoid tester rather than a high impedance multimeter to
test for voltage between the hot and the conduit then that is a good
start. To be more certain you will have to power a load between the
ungrounded current carrying conductor (hot) and the conduit long enough
to obtain a stable voltage reading under load. The difference between
the no load voltage and the voltage across a known load would allow you
to compare the voltage drop in the Equipment Grounding Conductor with
the drop in the neutral. If the difference is marked then the Equipment
Grounding Conductor pathway has a high resistance connection somewhere
along its run.
Well we aren't no thin blue heroes and yet we aren't no blackguards to.
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