Publication 1747-UM011G-EN-P - June 2008
Selecting Isolation 
Transformers
If there is high frequency conducted noise in or around your 
distribution equipment, use an isolation transformer in the ac line to 
the power supply. This type of transformer provides isolation from 
your power distribution system and is often used as a step down 
transformer to reduce line voltage. Any transformer used with the 
controller must have a sufficient power rating for its load. This power 
rating is generally expressed in voltamperes (VA).
To select an appropriate isolation transformer, calculate the power 
required by the chassis power supply(or supplies if more than one 
chassis in system) and any input circuits and output loads that are 
connected through this transformer.
You can find the power requirement (VA rating) for the chassis power 
supplies in the specifications startingon page 177. The power requirement for 
the input circuits is determined by the number of inputs, the operating voltage, 
and the nominal input current. The power requirement for output loads is 
determined by the number of outputs, the load voltage, and load current.
For example, if you have a 1746-P1 power supply, a 16-point ac input 
module, catalog number 1746-IA16, (12 mA at 120V ac) and a 16-point 
ac triac output module, catalog number 1746-OA16, (0.5A at 120V ac), 
the power consumed would be:
135VA + (16)(120V)(0.012 A) + (16)(120V)(0.5 A) = 1118VA
In general, we recommend that the transformer is oversized to 
provide some margin for line voltage variations and other factors. 
Typically a transformer that is 25% larger than the calculated VA is 
sufficient.
Most industrial environments are susceptible to power transients or 
spikes. To help insure fault-free operation and protection of 
1756-L55M24 1756-L55M24  

equipment, use suppression devices on power line to the equipment 
in addition to the isolation equipment.
IMPORTANT
In this case, 0.5 A is the maximum rating of the triac output at 30 
°C (86 °F). If the load draws less than 0.5 A, this figure may be 
reduced accordingly. The output portion of the VA calculation 
should reflect the current requirements of selected loads.Siemens Simodrive 6SN1112-1AC01-0AA1
Siemens Simodrive 6SN1146-1AB00-0BA0
Siemens Sinumerik 6FX1128-1BB00
Siemens Sinumerik 6FC5503-0AC00-0AA0 6FC5 503-0AC00-0AA0
Siemens Simatic 6ES5466-3LA11 6ES5 466-3LA11
Siemens Simatic 6FM1721-3AA20 6FM1 721-3AA20
Siemens 6SC6111-2AA00 
Siemens Simodrive 6SN1118-0BK11-0AA0
Siemens Simodrivel 6SN1123-1AB00-0CA0
Siemens Sinumerik 6FC5110-0DB03-0AA3 
Siemens Sirotec 6FR3110-0BA00-0AA0 6FR3 110-0BA00-0AA0
Siemens Sinumerik 6FC5247-0AF22-1AA0
Siemens Simatic 6ES7272-0AA30-0YA0 neu
Siemens Sinumerik 6FC5248-0AF02-0AA0
Siemens Sinumerik 6FC5203-0AF00-0AA0
Siemens Sinumerik 6EV3054-0GC 6EV 3054-0GC
Siemens Sinumerik 6EV3055-0AC
Siemens Simatic 6ES5246-4UA41 6ES5 246-4UA41
Siemens Simodrive 6SN1118-0DM13-0AA1
Siemens Simatic 6ES5946-3UA22 6ES5 946-3UA22
Siemens Sinumerik 6FC5357-0BB22-0AE0
Siemens Sinumerik 6FC5357-0BA21-0AE0
Siemens Sinumerik 6FC5410-0AX02-1AA0
Siemens Simodrive 6SC6100-0GB11
Siemens Sinumerik 6FC5357-0BA33-1AE0

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Siemens Simodrive 6SN1118-0DM33-0AA2
Siemens Simodrive 611 6SN1118-0DM33-0AA0
Siemens Sinumerik 6FC5357-0BA11-0AE0
Siemens Sinumerik 6FC5357-0BA10-0AE0
Siemens Simatic 6ES5928-3UB12 6ES5-928-3UB12
Siemens Simodrive 6SN1118-0DG21-0AA1
Siemens Sinumerik 6SN1122-0BA12-0AA0