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My question is twofold:
We have an electrical panel that has four wires coming into it from the outside. One wire is wrapped in white tape and goes to a terminal block where all white wires connect, this is obviously neutral. The other three wires terminate on three large lugs above all the breakers. One is wrapped in red tape, one in blue tape, and one left alone (black insulation). My question is, what is each of these three wires? Are they two hots (blue, red tape) and a ground? Or three hots? I always thought ground had to be green.
The second, related, part of my question is that we have a shared meter and want to measure our usage just for short time (a week or so). Can I clamp an ammeter on each phase and watch the current flow and make some calculations, or is there a clamp on device like a usage meter that one can buy relatively cheaply?
Thanks, Tom
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Tom, It sounds like you have 3 phase power coming into your breaker box....rather rare for most residential installations, but large subdivisions do provide this sometimes. Those three wires would all be "hot".
As for your second question, clamp around ammeters can give you a reading, but you would have to monitor each line and do it constantly for a long time. Utility meters work like this on large services. I'm not aware of any device that would be easy to hook onto your service to do what you want, but maybe someone else reading this may have an idea.
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Tom
The panel may be three phase, but in many parts the ground also has to have insulation on it. I believe to protect it from corrosion and damage.
If it is a ground it will be connected to a lug that is somewhat lower and off to the sides of the main lugs. The ground lug will also have no insulation or jacketing on it. This lug will be attached to a copper bar that in all likelyhood is at some point connected to the neutral. This is called bonding.
A few things to do.
1 - Where are the bare copper grounding conductors from each circuit connected back to? Usually they are connected to a grounding bar that is then attached with a jumper back to the ground bar where the large ground lug I discussed above is connected to.
2 - What are the voltage readings accross each of these wires? Read the following:
red to blue
red to unmarked
blue to unmarked
unmarked to neutral
3 - What area of the country are you in. There are parts of the country that are wired for 220 volt two phase. This is not a misprint - I said two phase. I have no idea how a panel is wired, but could find out. Two areas I know of are parts of Pennsylvania, and I believe areas in Louisianna.
What you want to measure your usage are current transformers (CT's). If you contact your local utility and ask for their metering and test department they can connect you with a loaner or rental unit. They usually take have them for industrial work, but if you ask right they might let you borrow one. I am forever amazed at how loosely these utilities are run; But it is probably a result of asset based billing - which is a long story.
-Rob
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Tom: Regarding measuring your electrical usage. It is easy to assume that if you know the voltage and if you measure the current, you'll get the power (Power = volts x amps). But that only works for DC and for AC resistive loads (light bulbs, electric water heaters, electric heaters) and in all all-electric home is going to be pretty close. But for inductive loads (motors such as your refridgerator, air conditioner, washing machine, etc.), the voltage and amperage can be out of phase and to be accurate, you want the intergral of volts x amps x dt (differential of time, not my initials). The electric meter from the power company does that. It totalizes all the instantanous power.
An aside: This used to be done with a clever clockwork mechanism that operated two pendelums in time with the power and current. The pendelums multipled like scalars (normal numbers) when in phase but would multiply to zero when completely out of phase (two perpendicular vectors). That's why you could shut off your meter with a big magnet. Now it is all done with solid state electronics.
Borrow or buy one like theirs (about $100 when I last bought one, but they are hard to find retail). I like the idea of asking your utility to borrow their meter. -David
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My question is twofold:
We have an electrical panel that has four wires coming into it from the outside. One wire is wrapped in white tape and goes to a terminal block where all white wires connect, this is obviously neutral. The other three wires terminate on three large lugs above all the breakers. One is wrapped in red tape, one in blue tape, and one left alone (black insulation). My question is, what is each of these three wires? Are they two hots (blue, red tape) and a ground? Or three hots? I always thought ground had to be green.
The second, related, part of my question is that we have a shared meter and want to measure our usage just for short time (a week or so). Can I clamp an ammeter on each phase and watch the current flow and make some calculations, or is there a clamp on device like a usage meter that one can buy relatively cheaply?
Thanks, Tom