I assume the existing disco lighting has a 13A plug top.
It's possible.
But you will need to calculate whether a 5A fuse is enough to supply the load of your theatre lighting rig.
Most 5a plugs do not have a fuse. 15a (also no fuse in plug) are more standard in theatre.
They are also usually connected to dimmers (which should have a fuse think radial circuits).
Depends on your disco kit, it may not like being plugged into dimmers. You really want a switch pack. If you are lucky, there may be a patch bay and you can then feed the circuit with hot power (theatre term for normal non dimmed power).
More info is really needed as "theatre lighting rig" means nothing.
can you post a pic of said socket, 5A was common previously, and still exists in some small community theares and halls, so not impossible.
Most stuff is 15A round pin now.
what disco light is it? and what dimmers are you using, some are more suited to lighter loads than others, if it really is a 5A socket, I would be thinking it would be somthing along the lines of an mini2 pack or similar.
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