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Question about tapping power cord to power volt/watt meter

Question about tapping power cord to power volt/watt meter

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  #1  
Old 09-03-07, 09:52 AM
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Question about tapping power cord to power volt/watt meter

I am building a box to house a voltmeter/wattmeter for my generator. The digital watt meter is made by Reliance Controls and requires 120v for power and also to measure the voltage. Current transformers to measure the amperage.

I have a 50amp/6 gauage cord that plugs into the transfer switch from the generator.

My plan is to pass the cable through the box (modified inlet box) where it will be spliced so I can install the current transformers.

My question is can I tap this 6 gauge wire to power the meter? The meter instructions say to use at least 16 gauge wire.

What I am not sure of what happens when there is a 40-45amp load on this 6 gauge cord. Will the amps go into the meter and blow it out?
 
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  #2  
Old 09-03-07, 11:03 AM
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An ammeter isn't hooked in series with any load, so it won't blow the meter.

Does your generator put out 220 V? If so, is your ammeter rated for 220?

I'm concerned about a full 50 amps being available to run the meter its self, though. I don't think it'd be safe to tap off of the 50 amp wires to run a meter without fuse / circuit breaker protection at about 10 amps (for 16 AWG wire). You don't want the power supply to the meter to be unprotected (or protected at 50 amps).
 
  #3  
Old 09-03-07, 12:02 PM
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Yes, it's 220v.

The meter has two 120v inputs to measure voltage on each hot leg. It also needs the power to light up the LED's.

Right now it does not have any protection besides the 50amp breaker on the generator.
 
  #4  
Old 09-03-07, 05:48 PM
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Is this what you have?

http://www.nooutage.com/meterpnl1.htm

You may use in-line fuse holders from the #6 generator leads to power the meter and also sense the voltage. Be sure the fuse holders are rated for use at 120/240 volts AC and use no more than a five ampere fuse. Probably a one ampere fuse would be fine.

I'm surprised that the instructions don't specify the size fuse and the silly thing should come with fuse holders.

Be sure to use a fuse in EACH "hot" lead.

Also, be sure to NEVER disconnect the leads from the current transformer when the power is energized. Do NOT install fuses in the leads from the current transformers. If you need to use this unit with the ammeter / watt meter disconnected be sure to short the two leads of the current transformer together. Yes, I said short them together.
 
  #5  
Old 09-04-07, 07:08 AM
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Yes that is the meter I have.

I wish I could find the instructions but I do remember it stating something about using a fuse or circuit breaker if code requires it but it did not come with any thing besides the meter and the two current transformers.

The connections on the back are all flat metal prongs. I had to install some of those crimp on disconnects on the wire to push onto the metal prongs.

Would I need to feed 6 gauge wire into the fuse and then the smaller gauge into the meter? I don't think a 5 or 1 amp fuse would take a wire that big.

I currently have 14 gauge wire to power the meter.
 
  #6  
Old 09-04-07, 09:04 AM
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When I read at the site: "Hinged front cover is supplied ready for cutting rectangular hole to mount meter. - and - Note that this product ships from two different locations. The electronic meter ships direct to you from the factory in Wisconsin. After it ships, the balance of the parts ship from Maryland" I got a clue what was going on. My bet is the company is just having the basic meter dropped shipped from the manufacturer. They are throwing in a few parts but are leaving you to do the modifications and building the unit.

Sounds kind of fly by night. I doubt they know much about what they are selling. Personally I'd look for a company selling a complete ready to go unit that could give you some real help if you need it..
 
  #7  
Old 09-04-07, 01:24 PM
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Put a suitable fuse inline with your meter power cord and tap the cord inside the box you are building.
 
  #8  
Old 09-04-07, 04:46 PM
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"Personally I'd look for a company selling a complete ready to go unit that could give you some real help if you need it.."

I have checked around but have found nothing that would work for me so that's why I am doing it custom.

I will go pick up a few fuse holders and fuses and put them on power wires feeding the meter.
 
  #9  
Old 09-04-07, 04:59 PM
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"I have checked around but have found nothing that would work for me so that's why I am doing it custom."


Remember, doing it custom means that you have no safety certification like that provided by CSA (in Canada) or Underwriters Labratories. Insurance companies and / or your generator manufacturer may not like this
 
  #10  
Old 09-04-07, 08:59 PM
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You will need to tap each line from your generator. Depending on "how" you are installing the current transformers you can probably use split bolts to tap off of the generator leads to the power meter.

You will need to have taps from each of the two "hot" leads along with the neutral lead. The fuses go in the "hot" leads and no fuse in the neutral. If you use the split bolts then also pick up a roll of "scotchfill" splicing compound to cushion the split bolts before final taping. It's a good idea to first wrap a layer or two of plastic tape over the split bolts with the adhesive side outward before using the scotchfill or the scotchfill will vulcanize to the split bolt and if you ever have to take it apart you will have a devil of a time.

Also, if you are installing this in a metal box you need to ground the box and cover to the equipment grounding conductor of your generator and transfer panel.
 
  #11  
Old 09-05-07, 06:41 AM
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I've designed many electrical boxes

let me give some comments here. First off, I think this is a great project for those that have emergency generators,and some electrical and assembly skills. I can tell you first hand, that load management during/after a power crisis can be trial and error, usually resulting in tripped genset breakers, and suddenly dark homes, etc. This type of monitor system would have great advantage, especially for those "pushing" their generator and not readily knowing all the wattages of the appliances that may be operating.

Here are a few rules that you might want to consider when buying, laying out, and wiring a metal box, containing hazardous voltages.
*yes, bond the box to a grounding conductor, and if the swinging door of the box is holding anything that connects to high voltage, then ground the door also, using flexible conductors, not depending on the door hinges, etc for conduction.
*Do not rely on any soldered connections for any part of the grounding conductors. This will increase the chances of a grounded box in the event of a fire.
*buy a NEMA rated box, NEMA1 at least provides for some protection when the door is closed. Also, find a box that has a removable inner plate, when you need to mount terminals, etc, that makes it much easier to drill, etc.
*make sure any high voltage on the door is "touch-proof". A swinging door is very hazardous with the power on and there is HV exposed. NEMA 12 gets you dust tite, NEMA4 gets out outdoor rating.
*make sure the door requires some type of tool for opening, to keep little hands out of harms way.
*I would tend not to use split bolts in a cabinent, since you need to somehow insulate this connection, and that increases a shock hazard in close quarters. I would use crimp ring terminals, terminal strip, and a insulated cover. This assumes you can crimp larger conductors successfully.
*I would NOT mount anything like this to an actual generator, vibration would do bad things to ordinary designs.
good luck!
 
  #12  
Old 09-05-07, 09:34 AM
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Originally Posted by ray2047 View Post
When I read at the site: "Hinged front cover is
Sounds kind of fly by night. I doubt they know much about what they are selling.
..
Actually, they (nooutage.com) have been around a long time, and if you call them up, they do know what they are doing.

That being said, a 'plug and play' model is available. I have NO idea how it works, but it simply plugs in to a wall outlet and reads the percent of load on the generator (according to the text).

Pre-assembled versions of these meter panels are available as well on other websites. I would have chosen analog over digital, but that's just me.
 
  #13  
Old 09-05-07, 03:32 PM
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In reference to telecom guy's post...There is nothing wrong with using split bolt connectors PROVIDED that they are properly padded with an approved insulating compound such as the Scotchfill that I recommended. (It may be spelled Scotchfil, however it is spelled it is a product of 3M.)

That said, I would certainly agree that a terminal block that could accept #6 conductors both in and out along with another tap for the smaller gauge wire would be preferable however such a terminal block would be far more expensive than the split bolts and Scotchfill.

Probably the most important thing I left out is to be sure to use a box that has enough room to hold all the wires, fuseholders, current transformers, splices and display unit without crowding.
 
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