Sorry for the delay, I've been running at 150% mod trying to keep up with work and home, so lists got shunted to the sidelines for a bit!
As others have said, every manufacturer has a different approach and how the modules will react also varies. Ours work in this sequence...
Original AMPFET series:
1-10kW, modules are NOT hot pluggable. They are connected in series and pulling a module hot results in some pretty spectacular fireworks.
25 and 50kW modules are as Fossil indicated - there is a bank of toggle switches on the control panel that each power down a block of four modules, then on the rear of the transmitter you use another toggle switch to short the output of the module you wish to remove, so that the combiner coil for that module acts as a load to the rest of the transmitter. The shorted module can then be removed when the transmitter is running. The only catch to this is if somebody had previously powered up a module that had the switch in the SHORT position and blew the switch - in that case, you'll have a cool blue flame arcing out of the connector when you remove it from the module you thought you shorted. Always a fun time...
AMPFET ND series:
The original 5 and 10kW versions (have current meters on the power modules) had a similar configuration to the 25 and 50 above - an ON/OFF switch for the power supply to each module, then a SHORT/OPERATE switch on the combiner input for each module. Same possibility for blue flame if the SHORT switch was failed.
The ND series models from 2.5-10 kW that have no current meters, just alarm LED's, on the power modules, have only a simple ON/OFF switch for the power supply to each module - switching off the supply for the module engages a relay that shorts the module output. Again, if the relay or relay driver circuit is defective, you could have problems, but these have proven to be much more reliable than the original toggle switches, as user error caused more failures than component problems ever did.
The ND25 and ND50 transmitters had a bank of circuit breakers on the rear of each power supply cabinet so you could power down the module to be removed. Then on the module there is a CHARGE/DISCHARGE switch to enable you to do a fast discharge of the power supply caps on the module (these transmitters have 120,000 uF of capacitance on each module, so fast discharge is necessary!). This also drops in the relay to short the output, as with the smaller transmitters.
The XL series had an inhibit switch on the front of the module which dropped the relay across the output, then when you disconnected the drive connector it broke an interlock circuit that operated the shorting relay on the module output - failure rate even lower now, as the switch is right above the connector so less chance of forgetting to press it.
Operates the same as the XL series, but with failsafes installed to ensure that even if you forgot to push the inhibit switch, the module would be protected from catastrophic failure, although it might blow an amp or two when disconnected.
NX (current production model):
Drive is via RJ45 as digital data - unplugging the front panel RJ45 connector disables the module and shorts the output, there are no switches to remember - so far not a single failure as a result of module removal.
That's it in a nutshell, except for the J1000, which has a hybrid combined output and must be shut down for module removal, and the ND1, which only had one power module anyway, so also must be shut down. Hope it helps!
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