Diode Decoupling

... perhaps like this:

Regards Uwe

It's completely non-standard wording. Normally "feed Voltages" (for power) are not referred to as control Voltages; so, if there are separate control signals Uwe's guessed meaning would probably not fit.

If there is no selection or control signal, then I would assume that they are merely after passive redundancy. But if the supplies are not centrally ground referenced, the customer could be concerned that a failing supply terminal may short to ground - so they may require bridge isolation instead of single-ended.

If it is a redundant control system, where the two controllers are fed from separate supplies, they may require diode on the control outputs, so that the systems are truly independent right up to the point where the signal goes to the user's control input terminal. In this case it can make sense for sensitive control points (either inputs or outputs) to be isolated from damage that could be caused when the other unit fails. Diodes feeding pull-down (or pull-up) resistors (the diodes having breakdown Voltage margin beyond the worst-case failure Voltages) would often be used in these situations.

If having read CR4's guesses and re-read the customer specification you are still uncertain what is meant, ask for clarification. In any event, send back your carefully written version of the specification as part of your tender; include as much information about your solution as is necessary to make your objectives clear, but not so much that it would assist your competitors to copy your solution.
Oh, and keep us posted.

I found the term "feed voltagees" very often in connection with power supplies, not only in low (example: memory supplies from backup and mains) but also for (up to very) high power inverters. So I think its a simple redundancy function if one supply fails.
Regards Uwe

Indeed, I had is no problem with the "feed Voltages" bit.

My problem is that the quoted clause from the specification refers to "control Voltages" as being "diode decoupled", which implies they are distinct from the feed Voltages. In this case I would tend to agree that it is unlikely to be relevant that the usual meaning for "diode decoupled (power supplies)" is different from this is probably not relevant here].

Even if it is simple redundancy that is required, the contractor needs to clarify polarity - and also the level of protection required [we need to bear in mind that some hi-rel applications use pseudo-floating subsystems that require bridge-connection of the redundancy]

Let me to explain the case.

Control circuit of LV switchgear contains protection relays, circuit breakers' making and tripping coils, signal lamps, auxiliary relays, timers and ....

All of them are fed from 220v DC power supply which is fed to LV switchgear by costumer. For reliability the costumer will consider to separate 220V DC feeding lines.

If there is no electronics based intelligence, Uwe's suggestion seems most likely. The required polarity and grounding arrangements should be apparent from the remainder of the customer description - but I would still be specific about any arrangement in the quotation (as Uwe showed, a picture here is worth thousands of words).

Rgds

Fyz

Abbas, tenders and quotations are always critical in a certain sense:

Our answers on your question do only show wahat WE think might be - they never doubtless show what your CUSTOMER might have thought. If there are such questions, I would recommend to clarify such a point directly with your customer.

Requests also sometimes have verbal "predeterminated breaking points" to find out, whether "its your meat" to answer correctly and get the order.

In my practical experience with customers I have always found that those who do not know what they want will never get satisfied with what they get - and that can be dangerous for fulfilling the order without trouble.

So - talk with the right ones. Good luck !!
Regards Uwe