Mueller+Ziegler Current transformers

Current transformers are vital switchgear components – safe, robust and precise!

Our current transformers enable the post-processing of currents by converting high alternating currents into a galvanically isolated alternating current of 5 A or 1 A.

The product range includes plug-in, wound current, split core and summation current transformers in accuracy classes 1 and 0.5. Higher accuracy levels and certified current transformers are also available on request.


Current transformers are special-type transformers which are used to transform a relatively high alternating current into an impressed alternating current of 5 A or 1 A. Due to their electromagnetic principle, they allow for achieving the galvanical isolation of the primary circuit from the measuring circuit. Phase balance and proportionality exists between primary and secondary circuit.

Technical data

  • Low-voltage current transformers according to DIN EN 60044-1, DIN 42 600, IEC 185 and DIN EN 61 010 part 1
  • Maximum operating voltage 720 V, test voltage 3 kV
  • Frequency 50-60 Hz (16 2/3 Hz and 400 Hz on request)
  • Overcurrent limiting factor1 FS to 1500 A, FS 10 from 1600 A
  • Thermal rated continuous current2 Id = 1,0 x IN
  • Thermal rated short-time current3 Ith = 60 x IN (1 s)
  • Dynamic rated current4 Idyn = 2.5 x Ith for wound primary type current transformers and Idyn = 100 kA for all other types
  • Insulation class E
  • Housing, polycarbonate black, self-extinguishing according to UL 94 V 0
  • Washer-and-screw assemblies M 5 x 10 mm

Special notes

For current transformers, the rated power available at the secondary terminals is indicated in VA. The selection of the rated power is determined by the consumption of the connected measuring instruments as well as its input lead. Especially for secondary currents of 5 A combined with long input lead, considerable power loss occurs (see also diagram on page 219). In this case, current transformers with sec. 1 A are recommended.

In case of plug-in current transformers, also the output rating in VA drops with decreasing transformation ratio. By winding the primary conductor several times, a smaller transformation may be obtained while the output power (VA) remains unchanged.

Example: 50/5 A 1,5 VA class 1, threading the primary conductor five times results in a current transformer with 10/5 A 1.5 VA class 1.

As compared to wound current transformers, this measure allows for considerable cost savings.

Grounding of secondary terminals:

According to VDE 0141, paragraph 5.3.4, current and voltage transformers should be grounded starting from measuring voltages of ≥ 3.6 kV. In case of low voltages (up to a measuring voltage of ≤ 1.2 kV), no grounding is necessary unless the transformer housing has large accessible metal surfaces.

Mueller+Ziegler current transformers - Product list








Wound current transformers

Transformer width 70 mm

Primary connection with M5 screws at transformer head

Weight approx. 440 g with foot fastening bracket with terminal cover



Transformer width 60 mm

Primary connection at copper rail 20 x 5 mm

Weight approx. 580 g with foot fastening bracket with secondary terminal cover



Summation current transformers

For the summation of two or three main transformers.

In case of different main transformer ratios, these must be specified in the order.

Weight 550 g

with foot fastening bracket

with secondary terminal cover