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Multi Ratio Current Transformer  CT(3)

dmapower (Electrical) (OP) 
7 Sep 07 14:00 
Hi; What would be the standard ratios for a CT Multi Ratio CT4000/5
Thanks,
DMA 

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. 

scottf (Electrical) 
7 Sep 07 20:27 
500/1000/1500/2000/2500/3000/3500/4000:5A
I don't remember the tap combinations off the top of my head :)


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 

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 ? 

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

jghrist (Electrical) 
10 Sep 07 17:27 
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. 

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

jghrist is correct, away from the device is what I should have said. NEMA SG4 details this for outdoor breakers. 

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. 

jghrist (Electrical) 
11 Sep 07 8:36 

scottf (Electrical) 
11 Sep 07 9:11 
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.




