Change Over Switch

30 of the 1 pole double throw relays is actually likely the least expensive, but is fraught with the dangers of what happens if only one goes bad.

I would use what are called "Machine Tool Relays", far more reliable and they can handle up to 12 poles. Your configuration would still require multiple relays because the 12 poles are all single throw, so you only get 6 DT poles per relay. But I would also have a master-slave arrangment, where you control only one relay, IT then controls the others.

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Relay 1 (Master, 8 pole) = 5 NO contacts feeding the coils of Relays 2, 3, 4, 5 and 6.

Relay 2 through 6 (slaves, 12 pole each) = 6 sets of CO (Change Over; 1NO, 1NC)contacts for your control stations, 30 total.

How about wiring both up permanently, with a lockout bag/barrier to prevent use of the idle item?

You don't say what load current or voltage (AC or DC, or level) the loads operate at, only that 24v AC is available in the panel.

If AC, have you considered using Triacs for this purpose.

If you use AC for the supply then the devices will switch off within the first half cycle after the gate is de-energised - highly inductive loads may pose a switch off problem, but this can be mitigated with an appropriate snubber circuit.

No relays will be required, but you will need 30 Triacs for each cable with a common gate feed for each set of 30.

Energising either gate circuit would switch on the relevant set of Triacs, which would remain in conduction until either the gate is isolated or the supply is removed

Depending on the load and supply voltage, they may be far cheaper and definitely more reliable than relays.

Heat sinking may be required for heavier loads.

Having said all of that, if you require guaranteed electrical isolation of the separate circuits for handling purposes then the relay or other mechanical switching methods would be preferential.

One could always replace the pendant with a piece of string and hang the remote on it from time to time.

If your controls require that the swap is complete and does not tolerate the case of having any one contact not changing over, then apply this method, if using multiple relays to cover the 30 contacts:

Suppose that you have relays each with n number of Change/Over contacts (example n = 4). You should use one of the C/overs, on each relay, connected in series on all of them, in such a way that the control power does not reach the part of the circuit doing the actuations, unless all the contacts in series, are closed ( for both cases). This means using an extra relay/contactor to supply the circuit.

The Swapping relays will have their supply before the extra relay/contactor, and controled by a switch (?!).

With n = 4, you will need 10 relays + the extra one relay/contactor.

Depending on the currents being switched, you might get relays with more than 4 c/overs.

I would suggest a simple PLC which can eliminate the need for relays and changeover switch. If you could send the details of 30 wire connections to the pendant and how they are connected to the control circuit, I might be able to tell how a PLC can achieve this.

Chances are if Anonymous Poster#1 cannot figure out how to do this with electromechanical components, then using a PLC is likely WAY beyond his skill set, not only for initial installation but for future troubleshooting. Plus, pendant control often indicates cranes or other moving machinery, and safety becomes more complex if you have a PLC (again, assuming a skill set that could not include a Safety PLC). You or I might choose to do it this way, but I have had bad experiences applying PLCs in applications where the users are not sophisticated enough, even when I do all of the initial programming and commissioning.

Why do you not...

Permanently wire both control systems, then add a simple selector switch on the console that select which method is active, the selector switch will then kill the contol power going to the different control switches. That way, only one set of pushbuttones/switches is energized at a given time.

If this is for crane control, I would seriously look at the legal and safety implications before doing anything.