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# Multi Ratio Current Transformer - CT3

## Multi Ratio Current Transformer - CT

(OP)
Hi;
What would be the standard ratios for a CT Multi Ratio CT-4000/5

Thanks,

DMA

### RE: Multi Ratio Current Transformer - CT

500, 1500, 1000, and 1000:5 from X1 to 2, and 2 to 3 and so on. Other ratios are derivable from those. ANSI/NEMA/IEEE assumed, don't know if IEC is the same.

### RE: Multi Ratio Current Transformer - CT

500/1000/1500/2000/2500/3000/3500/4000:5A

I don't remember the tap combinations off the top of my head :)

### RE: Multi Ratio Current Transformer - CT

Interesting. I never looked at how turns ratios add up on CTs. I went to a document I found in my old files and found the datat below. With this info, you can figure the turns ratio between any two terminals. e.g., on a 600:5, the ratio for tapping beween X2 and X4 is (50+250):5 or 300:5.

600:5
X1:X2  20 turns  x 5 =  100:5
X2:X3  10 turns  x 5 =   50:5
X3:X4  50 turns  x 5 =  250:5
X4:X5  40 turns  x 5 =  200:5

1200:5
X1:X2   40 turns  x 5 =  200:5
X2:X3   20 turns  x 5 =  100:5
X3:X4  100 turns  x 5 =  500:5
X4:X5   80 turns  x 5 =  400:5

2000:5
X1:X2   80 turns  x 5 =  400:5
X2:X3  160 turns  x 5 =  800:5
X3:X4   60 turns  x 5 =  300:5
X4:X5  100 turns  x 5 =  500:5

3000:5
X1:X2  200 turns  x 5 = 1000:5
X2:X3  240 turns  x 5 = 1200:5
X3:X4   60 turns  x 5 =  300:5
X4:X5  100 turns  x 5 =  500:5

4000:5
X1:X2  100 turns  x 5 =  500:5
X2:X3  300 turns  x 5 = 1500:5
X3:X4  200 turns  x 5 = 1000:5
X4:X5  200 turns  x 5 = 1000:5

5000:
X1:X2  300 turns  x 5 = 1500:5
X2:X3  100 turns  x 5 =  500:5
X3:X4  400 turns  x 5 = 2000:5
X4:X5  200 turns  x 5 = 1000:5

### RE: Multi Ratio Current Transformer - CT

Just as a side issue, what is the standard with regards to P1 & P2
ie is it the standard to have P1 nearest to the source ?

### RE: Multi Ratio Current Transformer - CT

In the case of BCTs on devices, the primary polarity is toward the device.

### RE: Multi Ratio Current Transformer - CT

I'll have to disagree with stevenal.  On circuit breakers and transformers I've seen in the USA, the polarity marks of bushing CTs have been away from the device.  I don't know if there is a standard for this.

### RE: Multi Ratio Current Transformer - CT

In switchgear with CTs on the bushings of drawout breakers, primary polarity is toward the breaker.

### RE: Multi Ratio Current Transformer - CT

jghrist is correct, away from the device is what I should have said. NEMA SG-4 details this for outdoor breakers.

### RE: Multi Ratio Current Transformer - CT

Sorry to barge in on this one, but is there a specific IEEE standard that lists standard CT ratios?

Thanks,

Richard Byrne.

Richard Byrne, E.E.T.

ANSI/IEEE C57.13

### RE: Multi Ratio Current Transformer - CT

Confirm for the BCTs and other CTs we make for apparatus, the polarity is normally away from the device, i.e. on the top for a BCT.

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