Voltage locations in MEP-003 control cubicle

[Crawdaddy]

I'm working on installing a set of JimC's volt/amp gauges and I'm looking for a good place to pick up the voltages for the gauges. I'm hoping to pick up L1 and L3 separately so I can see the 120v on each leg to look for imbalance. I know I could pick them up out of the output box, but I imagine pulling them out of the control cubicle would result in an increased level of safety.

Looking at the wiring diagram, it looks like I can pull L1 and L3 off of terminals 15 and 12, respectively of the existing volts/amps switch(S. I know the neutral has got to be on that switch too, but I can't find it on the diagram. L0 seems to go everywhere. Are terminals 15 and 12 good clean feeds off of the genhead output, and where can I find L0? Perhaps I can get L0 off of the frequency gauge, I just need to meter it out.

 

[Triple Jim]

Sort of related to your question, and maybe you know this, but to watch for load balance, you're better off monitoring current than voltage.

You should be able to get L0 from the neutral terminal of the convenience outlet, as one example. I bet if you ask Jim C., he'll let you know what he had in mind.

 

[Crawdaddy]

For the amps part of the equation, there's a choke that goes over the L1 and L3 wires to send a signal to the gauge. For the voltage, he suggests tapping off the old frequency gauge, which gives 240. I'm trying to monitor each leg of 120 separately and then derive the 240 voltage from addition of the 2 legs toghether.

 

[Triple Jim]

If I understand correctly, you want to measure the voltage of each 120v leg separately. If you do, I think you'll see them pretty much the same, all the time, since there is only a small drop in voltage with increased load. Measuring the current on each leg separately and being able to switch to display each one will tell you how well your loads are balanced. As I remember, you can do that with stock wiring, because with the front panel meter selector switch, I can make the current meter show L1 or L3 as desired.

My apology if I'm missing your point entirely.

 

[Crawdaddy]

I bought JimC's gauge kit, which includes all digital gauges that include frequency, and 2 amps/volts combo gauges. It replaces all the existing gauges except for DC voltage and the hourmeter. In Jim's classifieds ad picture, both volt gauges showed 250 volts because he used the frequency transducer input wires to get the voltage. Showing the exact same voltage twice isn't as handy as showing each leg's voltage independently. Yes, measuring current is a more accurate way of showing amps, which is why the other half of the gauge shows that. Knowing the voltage of both of the legs is just more data to help show and diagnose unbalanced legs.

But in the end, I'm just looking to not see the same number twice on the gauges...

 

[Triple Jim]

OK, I understand things better now. Check this with a meter, but I'm pretty sure one side of transformer T1's primary is L0. Same with T2.

 

[Jimc]

yes, in those pictures i did just a quick hookup just to see them working. the best way is to set these up to monitor voltage and current on each hot leg. this would normally show 120 as the voltage reading. i connect them to the input side of the main breaker. this way they are on when the generator is running and you are getting a reading as close to the output lugs as possible. i personally prefer to not pickup any voltage or current from other sources because you could end up having a bad connection at some point or something just fails then the gauges dont work or arent giving you a correct reading for what is actually on the main lugs. now your tracing wires and trying to figure out whats wrong. of course this will happen when your power is out and you need the generator. i want to leave as much of the generator portion out of the equation and just want to monitor the mains. i like to think of these gauges less as an integrated component and more like a multimeter that is separate from the system. if i am not mistaken the main breaker is 3pole and it should be something like L1/N/L0. neutral is in the middle, the outer two are hot. cant remember which one is which at the moment. the red 1/4" eye connectors in the kit are sized to go on the studs on the back of the main breaker. the pickup coils should slip right on to the heavy main wires going to the lugs. as jim said you want to use the current portion to load balance.

 

[Crawdaddy]

As of now, with some quick probing around the control cubicle and being lazy, I've found where I'm going to monitor the voltage from. One meter will pull 120v off the input side of the frequency transducer. The other is pulling 240v off the lines that went to the original voltage gauge with the knob on the front panel turned to the L1-L3 position. I can also turn the knob to read 120 in the L3-L0 position.

I have no clue whether the transducer happens to read off L1-L0; I suspect it also reads L3-L0, since that would always yield 120V in any mode. Unfortunately that means I don't get to see 120v on the other leg, but some simple subtraction can tell me what the other leg measures for voltage. Amps measurement will always be accurate for both legs of the set thanks to the bottom half of the gauges.