CT Polarity dots
- Thread starter Zyb
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4x4dually
Senior Member
- Location
- Stillwater, OK
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- Electrical Engineer/ Ex-Electrician
This is one of the more recent diagrams I've drafted. I tend to veer from the standards if it helps our assembly floor understand better. I'm no expert in symbol usage but this is how I did it. 
4x4dually
Senior Member
- Location
- Stillwater, OK
- Occupation
- Electrical Engineer/ Ex-Electrician
The polarity marking is certainly optional and the way I look at drawings, the less amount of things on the drawing, the less amount of things to check or things to be wrong on one that I have to go back and fix on a released drawing later. If you add polarity to the schematic, ask yourself if it is really necessary and does it help the installation or user. If not, then leave it off. The amount of time drawings go back and forth through drafting and checking is enough as it is IMO. Anything to reduce errors is good. I'd rather have less info that is 100% correct, than too much if some of it is wrong. $.02
Does the actual CT device you are using have any polarity dots or marks on them?
Does the actual CT device you are using have any polarity dots or marks on them?
Thank you 4x4, it's the inspector that is asking for the dot on the map. I just want to make sure that I understand it right. Yes it has a mark
4x4dually
Senior Member
- Location
- Stillwater, OK
- Occupation
- Electrical Engineer/ Ex-Electrician
Roger that. Good luck.
Google “Dot convention”, go to images, and pick which one you like the best.
I don’t see anything wrong with what you have in post 3, other than the way you have it on the PV system.
your metering or phasors will show incoming power or phasors that line up rather than exported power Where the phasors show the current 180 degrees form the voltage.
I don’t see anything wrong with what you have in post 3, other than the way you have it on the PV system.
your metering or phasors will show incoming power or phasors that line up rather than exported power Where the phasors show the current 180 degrees form the voltage.
jaggedben
Senior Member
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- Northern California
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- Solar and Energy Storage Installer
They had better or they'd be nearly useless.
Carultch
Senior Member
- Location
- Massachusetts
They either have colored wire to tell output leads apart, or the terminals marked X1 and X2. The typical color code I've seen is white for X1 and black for X2. The X1 and X2 wires then get connected to I_x1 and I_x2 respectively as it is marked on the meter, where little "x" would be filled in with the designation of each corresponding phase (either A/B/C or 1/2/3). There's also a "this side to source" label, or arrow label of intended current flow direction through its opening, so that it counts power flow in that direction as positive. By default, it would count reverse power as negative, unless the meter is designed otherwise to do something else with this information (e.g. ignore negative power, absolute value bars for "secure forward", separate kW-hr registers, etc).
CT polarity can be a case of "two wrongs make a right, when they are the right two wrongs". Mess up the orientation of the CT body on the wire, you can simply swap the two output wires, and the meter's measured result will be the same. It's best to get it correct, so you don't confuse others later on.
The bigger question is: which side counts as the source in an inverter application? And especially a battery application with intended bidirectional flow? This will depend on the audience of the meter data, and their standards. The norm I'm familiar with, is that a utility always counts the service as the source, such that consumption is positive and production is negative. While a customer-owned production meter that has nothing to do with the utility, would count production as positive.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
So far as I've seen the typical practice is to treat meter each source in the direction it outputs. So the arrow on 'Consumption' CTs faces away from the grid, and the arrow on solar CTs faces away from the solar. I'd expect CTs on the battery should face away from the battery.
But this is just convention as far as I've seen, it really doesn't matter as long as it agrees with the software setup and the installation instructions.
But this is just convention as far as I've seen, it really doesn't matter as long as it agrees with the software setup and the installation instructions.
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