paralleling Ammeter and Power Quality Meter off 1 set of CTs

[jbond]

Hi,

If you have some CT's feeding a few things in parallel, for example an ammeter, a power quality meter and perhaps another tarriff meter.

Then it seems to me that none would see the proper current from the CT as it would all be divided appropriately determined by the current division factor which is determined by the burden/impedances of those devices.

I mentioned it to someone, and he said its ok because a CT produces a voltage, and its actually the voltage that you are looking at. But that doesn't seem right to me, because then your result would be affected by the volt drop in the cable which is a variable dependent on the length of cable in the installation, which in turn would have to be entered into the parameters of the meters etc.

Can someone explain it to me a bit clearer? I'm a little fuzzy in the head on this one.

Thanks,
Matt.

 

[mrbrue]

Matt,

First, CTs feeding the meters must be in series, not parallel. Then, there's the overall burden on your meters. You need to sum up the overall burdens and cable lead resistances and make sure your CT burden (VA) is sufficient to drive the devices.

 

[RalphChristie]

You are correct, the meters have to be in series. Meters connected to CTs are current operated and not voltage operated.

Just note the comment of mrbrue regarding burdens.

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