English to Hebrew Tech/Engineering Engineering (general) water heating

It appears in the following sentence:
"The insulation resistance is assured by pre-ballast and post-ballasts".

There's also a drawing where pre-ballast seems to refer to 3 winding pipe elements before the wire heater and post-ballast seems to refer to 3 winding pipe elements after the heater.

The file is written in German English, so it's possible that some of the English terms are inaccurate.

I've seen what Wikipedia says, it's unhelpful.

Thanks in advance for your help!