PM8240 - TNS without a 4th current transformer

[Philippe_Morel]

Hi,

The net is TNS. So we choose 4W-Wye in the setup of the PM8240.

But there isn't a current transformer placed on the Neutral.

Now we see for I5 (ground?) 40A and for I4 (Neutral) 0A. But I4 should be around 40A.

The Compact NSX, placed upstream of the PM8240, shows around 40A for the Neutral.

1. How to wire the I4 terminals when we do not have a current transformer?

Like shown on screenshot 1A or like shown on screenshot 1B? Or is this not so important?

2. Where to tell the PM8240 that a fourth current transformer is not present and that it should calculate the Neutral? (This is possible with a PM5560.)

Thanks!

BR,

Philippe

[Yut]

Just simply connect I4+ and I4- together.

[DanL · Accepted solution]

If you have only 3CTs for a 3 phase system (with either 3 or 4 wires), you should use the "3CT" wiring diagram.

Ideally, one of the I4 terminals should be jumpered to the grounded CT common, but it should also work fine if I4 is not connected.

The "I5" measurement on the PM8240 is the calculated residual current of I1 + I2 + I3 + I4. So when I4 is not used (as shown above) and you have a 4wire system, this should be the neutral current.

If the I5 measurement is not your expected neutral current, you may have have a CT polarity, phase swap, or ground fault issue.

I recommend do NOT simply connect I4+ to I4- as it can become a loop antenna that may allow the meter to register when in close proximity to AC magnetic fields.

[Mannguyen]

I agreed with the remaining question from @Philippe_Morel and somebody may help me with this:

''2. Where to tell the PM8240 that a fourth current transformer is not present and that it should calculate the Neutral? (This is possible with a PM5560.)''. Thank you in advance.

[Charles_Murison]

Hello @Mannguyen ,

There is not way to tell the PM8000 meters that there is not 4th CT. Have a look at https://www.se.com/ca/en/faqs/FAQ000232697/ for more information on wiring options.

Regards,

Charles

[DanL]

The PM8240 will always both measure I4 and also calculate the residual of all measured inputs.

When you have only 3CTs directly connected to the meter's I1, I2, and I3 inputs:
- the residual is the Neutral current for a 4wire system (assuming no ground faults)

- the residual is the Ground current for a 3wire system