MEP-803a Measuring current on L1 in 120/240V

[BeStihl]

Has anyone attempted to alter the wiring to allow the ammeter to show current on L1 while in 120/240v? The operator manual shows it as an option. I can obviously check 240v on L3-L1 & current on L3, but when I switch to L3-L0 I get 120v on L3 & same current on L3, was wanting to monitor current on both L3 & L1 because a split phase system is never truly balanced unless it is running in 240v only. Just curious.

 

[kloppk]

The %Load meter doesn't actually display the current at the L3 lug in 120/240 mode.
The %Load meter is actually displaying the current provided by one of the 3 pairs of windings in the gen head.
In 120/240 mode the %Load will display the total load applied to L1 and L3 combined, not just L3.
The only time the %Load meter actually displays the load on each lug is when it's in 208 3 phase mode.

 

[BeStihl]

Thanks for the reply Kloppk.

I guess I can use my fluke amp clamp to monitor both legs, but it seems like I could route the output from the CT of L1 when the VM/AM is in the L3-L0 V/L3 A setting to actually monitor what’s going through L1 at the CT instead of L3.
I can measure with an amp clamp 40A on L3 & 45A on L1, but the PRC will show 80% because I believe it is only measuring L3 at the CT, when I switch to L3-L0 it shows the same load on L3. I will look further into the schematics to make sure.

I wanted to do the same to my MEP-017a but when in 240v mode current was measured on L3, and L2 was short circuited by the voltage selector switch. Maybe it’s not possible to monitor both legs (lines) going through the CT individually. Maybe it’s not worth the hassle to alter something, I just thought it would be sweet to be able to see the load on each leg.

 

[rickf]

Install separate meters for each leg. If you want to modify the unit that is the easiest and best way to get what you want without changing the wiring.

 

[Farmitall]

The current in any series circuit is the same in either leg.

Clamping your ammeter on L1 or L3 leg will give you the same reading.

 

[BeStihl]

120/240v is not a series circuit, it is a parallel/series circuit, the 240v only circuit is series and that statement above is true but when you add a neutral you have an alternative path for current to travel and with an imbalance that is when you get current on the Neutral.
Ex. 40A on Leg 3 & Leg 1 running a 240v heater, then add 10A on a 120V fan on L1, now you have 40A on L3 & 50A on L1. My question is in this scenario would the PRC read 40A or 50A?
Maybe I’m just making a big deal out of nothing I just didn’t want to be near max load and a 120V device push me into an overload situation without my knowledge, I guess I can load L1 only and verify that the PRC either reads it or not. Thanks for the replies gents!

 

[2Pbfeet]

120/240v is not a series circuit, it is a parallel/series circuit, the 240v only circuit is series and that statement above is true but when you add a neutral you have an alternative path for current to travel and with an imbalance that is when you get current on the Neutral.
Ex. 40A on Leg 3 & Leg 1 running a 240v heater, then add 10A on a 120V fan on L1, now you have 40A on L3 & 50A on L1. My question is in this scenario would the PRC read 40A or 50A?
Maybe I’m just making a big deal out of nothing I just didn’t want to be near max load and a 120V device push me into an overload situation without my knowledge, I guess I can load L1 only and verify that the PRC either reads it or not. Thanks for the replies gents!

If it is of concern, I think that It is straightforward to install a pair of aftermarket digital ammeters, or check with a clamp on meter.

 

[millerm13]

I have my 803a set up with two digital meters, one for each leg and use CT's to record amps on each leg. When load testing with an electric range they do show an imbalance between legs. but cycling the different burners and oven/broil can change the readings. Machine does not seem to care. I have seen 40 amps on each leg.

 

[BeStihl]

The %Load meter doesn't actually display the current at the L3 lug in 120/240 mode.
The %Load meter is actually displaying the current provided by one of the 3 pairs of windings in the gen head.
In 120/240 mode the %Load will display the total load applied to L1 and L3 combined, not just L3.
The only time the %Load meter actually displays the load on each lug is when it's in 208 3 phase mode.

I must apologize for not taking your word on this account. I ran my set tonight with an imbalance of 31A-L1 & 21A-L3and the PRC read 50% which would be about 25A on each leg, then I dropped the 120V load and monitored the set again it was reading 40% on the PRC with actual draw of 21A on both legs 1&3. So you are 100% correct, sorry for not taking your word I just have learned to prove things out. It does account for the combined load on each leg or set of windings. I assumed because the manual & writing on the AM/VM said L3 that it was only monitoring L3. I did take your advice and added the MOV to the AVR, so you gotta give me some credit. Thanks for the advice and I will bow out to the guru!