EKM Metering

I see on the meter configuration, under "Advanced" => "General" tab, settings for CT Ratio: 100A: 26.6mA. Are they available for sale? I am looking for CTs which are smaller then 13mm and can measure less current if possible, less then 1/4 amp current flow accuracy. The max current what my lines can get is 30 amp, so I should be even enough and safe at 50A CTs, but not sure if they exist and if it possible to configure them there.

Hello Riv,

We do not carry 100 amp CTs for the Omnimeters at this time. We have found that our 200 amp CTs are super accurate at the lower measured amperage ranges. You can find some 26.6mA output CTs on the web there but they are not 0.1% accurate (more like 1% accurate) so any gains you would have by going to a 100 amp CT would be lost.

If it were me I would use the 200 amp CTs we supply, you will find them to be quite good at 1/4 amp.

When using 200 amp CTs, the Omnimeter and CT combination is 1.0% accurate between 0.25 amps and 0.5 amps, above this current they are 0.5% accurate. The start current for the meter is 0.5 amps. The meter is still accurate under 0.25 amps, we just cannot certify it to be a known accuracy (below this you are talking about pennies worth of power per year).

We have connected a chain of 10 meters together in series with the only loads each meter was measuring was the meters downstream. Each meter draws less than a watt. In the chain we setup it was apparent that each meter would meter the meters downstream of it. We could see this because the pulse output light would flash in series with the first meter in the chain flashing faster than the second meter in the chain, and the second meter flashing faster than the third meter in the chain, etc.

Thanks,

Thank you Jameson,

I see, looks like I have to stay with your branded 200amp, just ordered bunch of them. I was looking for smaller version not only for accuracy and amp rating, but also actual CT size. Since I have fit 2 of them into inline enclosure such as Type C Conduit Body, and most common sold in HomeDepot are 3/4" size, when CT is require at least 1" or even 1-1/4" size, I just ordered both online to measure.



The question regarding approach to install, since we started to use them a lot in datacenter environment and most common power feed are used 208v/30amp, 2 hot (L-L) and 1 ground wires. Usually each rack has 2 separate feeds, so I am ending up with 4 hot wires and will end up installing 2 meters per rack.
- Should I still connect ground wire to meter neutral pin in this case?
- In case multiple racks, example 3 racks - we will end up with 6 feeds or 12 hot wires (120v L-N or 208v L-L). Can I connect only 4 meters in this case and will they measure right values per amp, kW and kWh readings?
- How is really bad to extend CT wire size? I need to get from 6' to something like 10'-15', but I am planing to use thicker wire, for example 18AWG. I am planning to shorter original wires from CT to a couple of inches, solder 18AWG wire instead.
- Original CT wires are twisted. Will it give any bad impact if new extended wires will be just straight, combined into single outer jacket with other CTs and voltage wires together? Something like Carol Super 18 AWG 6-7-10 Conductor SOOW cable.

Hello Riv,

Here are the spec sheets, including dimensions for our smallest solid core CT, and smallest split core CT:

BCT-013-200: http://documents.ekmmetering.com/EKM-BC ... -sheet.pdf

SCT-013-200: http://documents.ekmmetering.com/EKM-SC ... -sheet.pdf

most common power feed are used 208v/30amp, 2 hot (L-L) and 1 ground wires. Usually each rack has 2 separate feeds, so I am ending up with 4 hot wires and will end up installing 2 meters per rack.
- Should I still connect ground wire to meter neutral pin in this case?

No I would not substitute the ground wire for the Neutral. If you really only have 2 hot wires I would consider this a 208 volt 2 wire system, and so therefore you will only need 1 CT per install. This would be similar to a European system, you would use an Omnimeter and wire it like this: http://www.ekmmetering.com/information/ ... ml#answer5

Are you sure this is not a 120/208 system? In this case you would have a neutral available.
You say you have 2 separate feeds, you can either meter these separately or combine them (as long as you keep the hot wires that are on the same phase running through the same CT)

In case multiple racks, example 3 racks - we will end up with 6 feeds or 12 hot wires (120v L-N or 208v L-L). Can I connect only 4 meters in this case and will they measure right values per amp, kW and kWh readings?

From this it looks like you do have a neutral (so depending on the number of hots you have, you will need 2 or 3 CTs per meter). You can get away with using as few as 1 meter to measure this, or if you want to measure the racks or servers separately you can use more meters. This is because you can measure the parallel feeds. Let me know which you would like to do.

Hint: You can tell if two wires are on the same phase by using a volt meter. If you test the wires and they are on the same phase there will be no voltage between them. If the wires on on different phases or one is a hot and one is a neutral, you will have voltage (120, 208, 240 volts, etc)

How is really bad to extend CT wire size? I need to get from 6' to something like 10'-15', but I am planing to use thicker wire, for example 18AWG. I am planning to shorter original wires from CT to a couple of inches, solder 18AWG wire instead.

I would not extend the CT wires if I could help it.
If however you absolutely need to extend the CT wires, I would recommend that you pay close attention to the connections. I would solder the wire ends together and then use heat shrink tubing to seal the joint. We have found that we lose about 1% accuracy when we extended the CT wires by 50 feet. Using larger wire will not help with the accuracy loss.

- Original CT wires are twisted. Will it give any bad impact if new extended wires will be just straight, combined into single outer jacket with other CTs and voltage wires together? Something like Carol Super 18 AWG 6-7-10 Conductor SOOW cable.

No I do not believe the CT wires have to be twisted to remain accurate. Only the RS485 data wire needs to be twisted. The twisting of the wire keeps the RS485 signal clear.