Crompton Controls M20 - Manual (Page 18)

Emotron AB 01-2551-01r4 Selection of Current Transformer 17
6.2 Motors greater than 100 A
1. Check the rated motor current on the motor plate.
2. Compare this value with the current in Table 2.
3. Select the primary and secondary current transformer and the appropriate
number of windings from the columns in Table 2.
Please note that the ratio of the primary transformer must be exactly as provided
in the table below, otherwise the monitor power calculations will be inaccurate.
This will affect power readings, settings etc.
Example
• Rated motor current = 260 A.
• Select 251-500 A from the first column in Table 2.
• This gives:
- Primary transformer 500:5, 1 winding. (The motor wire is drawn through
the primary transformer once).
- CTM010 with 2 windings. (The wire from the primary transformer is
drawn through the hole in the CT, "CTM10", twice).
Table 2 CT greater than 100 A.
RATED MOTOR
CURRENT [A]
CURRENT TRANSFORMER TYPE and
NUMBER OF PRIMARY WINDINGS
101 – 150
150:5 + CTM 010
1 + 2
151 – 250
250:5 + CTM 010
1 + 2
251 – 500
500:5 + CTM 010
1 + 2
501 – 999
1000:5 + CTM 010
1 + 2
NOTE: Check that the appropriate Current Transformers has been ordered
and shipped with the M20. Contact the supplier if in doubt.