Harris Institute of Technical Training

Our engineering dept. sent out a 320 meter base, so I went to install a cl320 Fm2s in the service....well come to find out the service is 120/208 with a load cal of 400amps for this customer....so I can't put in a 12s because it is only a cl200, I looked in my All in One book and my only other option is to have the cusotmer change out the meter base so that I can install a Fm5s with 2 ct's any other suggestions on how to provide a metered service to this customer with out all this.
Thanks

Beth,
Does your company use any other Class 320 meter forms (e.g.,12 or 16)? If they do not use other Class 320 meters, is purchasing a Form 12S Class 320 meter an option (I believe they still make these)? The 5S with two CTs and all of that metering will work great but this option sounds like a big hassle.
Is this meter installation on a house?
If this is a house, is it being served by a three phase 120/208 volt, four wire transformer bank?
If you get a chance, please let me know the answer to these questions; I may be able to suggest a more efficient answer.
Take Care,
Brad

Brad,
The only CL320 we use is the Fm2s, I am going to check on lead time for ordering a Fm12s Cl320, your right that would solve the issue quickly, The installation is on a new Resturant going into the building, it is a three phase transformer bank but the customer only needed single phase due to all kitchen..etc...is being feed with gas. Let me know what you think!

Thanks
Beth

Beth,
Even though this customer is requiring a large single phase 120/208 volt network service to meet the electrical needs at the restaurant, the application of this service is an unnatural way to provide single phase voltage and service to this customer.

Any 120/208 volt network services fed from a 4 wire WYE 120/208 volt transformer bank should be evenly distributed between all combinations of energized phases and neutral: A,B,N – B,C,N – and C,A,N. Equally loaded and balanced energized phases and neutral is a more efficient way to use the WYE bank. When a large single phase, 400 amp 120/208 volt, network service is connected between one of these combinations, leaving the other two serving lesser load requirements, then this will make it so that the bank is unnaturally loaded across those two energized phases and the neutral. Serving the customer this way is not the end of the world and it won’t make a lot of difference in the long run, but it is not how network services are designed to be served. Also, WYE banks don’t usually have much neutral current, but because of how this bank is loaded in an unbalanced way, there will be some current flowing in the neutral conductor.

My more efficient answer (or suggestion) for you to share with your engineering department is: This customer has a large single phase load and even if the customer does not need three phase power, most often we may think that a single phase service is the only correct service to serve them. That’s not true. Because the 4 wire 120/208 volt WYE bank a customer, like the one you are trying to connect, should be served with a three phase service and a Form 16S installation. The 16S installation allows for better balance of the customer’s large amount of single phase loads to be distributed across the three phase conductors and the neutral. By doing it this way, it might make it so that the customer would not need a single phase 400 amp service, but rather be better served by a three phase 200 amp 16S installation.

For future consideration: Install a 16S and utilize all three phases as a more efficient use of the 4 wire WYE bank and does not cause the neutral current concern as discussed above. A further benefit of this type of 16S installation is that it allows for the flexibility of customer types at the location. For example: a new customer takes over the space and has three phase load requirements, you will already have the correct metering and service in place.
If you have any follow-up questions please let me know.
Take Care and Be Safe All Ways,
Brad

So instead of a much larger single phase transformer with a secondary rating of 120/208v (I didn't even know they made a single phase transformer with this voltage) you would use a three phase bank of 120/240v transformers (common) with the secondaries parrelleled and connected wye for a 3 phase 120/208v secondary service. Then the consumer could distribute all of its single phase 120v load along all three of the legs. Then you could use a self contained 15/16s meter instead of CTing the service. Sounds pretty cool.

Would this be more efficient than an single phase transformer? Would the total amperage be reduced somehow that a 400amp rated service could use a 200amp rated self contained meter?

Also, I believe a 400 amp single phase service can only be loaded up to 80% of its maximum rated capacity (320amps), so what would be wrong with using a cl320 2s meter?

Good stuff here, I've got a lot to learn in this trade.

Electrotech,
I am glad you are asking questions and participating in this comment thread. It’s nice to see enthusiasm for the craft and to see you have the understanding that there is much to know. I am happy to address your questions:
“So instead of a much larger single phase transformer with a secondary rating of 120/208v (I didn't even know they made a single phase transformer with this voltage)”
There is not a single phase transformer that will supply a 120/208 volt, three wire network service and system. Like you say, it requires a three phase, 120/208 volt, four wire WYE connected transformer bank to provide the 120/208 volt, three wire network service.

“Then the consumer could distribute all of its single phase 120v load along all three of the legs.”
The 120/208 volt network service allows for customers’ single phase loads that are both 120 and 208 volts, but does not have any provision for three phase loads. So, if the electrician who is doing the electrical work at this location does his or her part correctly, then the 120 and 208 volt single phase loads will be balanced across the three wire network service (along all three legs like you say).

“Would this be more efficient than a single phase transformer? Would the total amperage be reduced somehow that a 400amp rated service could use a 200amp rated self contained meter?”
As stated in earlier comments, the customer requires a 120/208 volt, three wire, 400 amp network service and system connection. This system can only be delivered from a 120/208 volt, four wire WYE connected transformer bank. It is not a question of efficiency in regards to whether using single or three phase banks (single phase and three phase kW being equal but three phase is more efficient). It is that the customers’ loads require 120 volts single phase and 208 volts single phase and the 120/208 volt, three wire network service will supply these loads correctly and completely.
The customers’ total connected load is a 400 amp service, but the Class 320, Form 12S meter that I suggested they purchase is only rated at 320 amps, which equates to 66.56 kW continuous and 83.2 kW @ 400 amps for short intervals. If they would have chosen to serve this customer with all three phases and the neutral using a Form 16S meter, then the continuous duty of the Class 200, 16S meter would have been 72.05 kW and the possibility of having three phase loads connected later on if necessary. So, maybe this would work fine and maybe it wouldn’t, but it would make it so that all three phases are used and the neutral current problem would no longer be an issue. In summary, loading a three phase, four wire, 120/208 volt WYE bank to 72.05kW and a 16S meter is a better and more efficient way to use the capacity of the bank.

“Also, I believe a 400 amp single phase service can only be loaded up to 80% of its maximum rated capacity (320amps), so what would be wrong with using a cl320 2s meter?”
The customer is being served by a 120/208, three wire “network” service which requires a Form 12S meter, so the Class 320 2S single phase meter is not the correct meter for this installation. That is why I suggested they use a Form 12S Class 320 meter to serve the customer rather than install CT metering.

Be Safe in your pursuits of metering. I am happy to assist you any way I can.

I had this problem once a few years ago. An entire building was brought to town on the barge in 6 pieces. The meter socket was a Form 2S 400 amp. There a a 500 kVA 208Y120 volt padmount about 10 feet from the meter base. There was no other option for the feed.
I did not find a CL320 Fm 12S meter although it became a moot point when I could't find the fifth jaw kit for the meter socket. The customer had to install a CT can with 2 CTS, a main disconnect and a Form 5S meter socket.