How would one tag multiple security camera’s mounted on a single pole like on the image below? I currently have 4 different camera’s and one utility_pole, but would like to show they are all connected.
The question seems to have already been asked on the talk page of the surveillance key as well as on other talk pages but seems to have been unanswered.
I’d love to know the same about street lamps and power poles.
In ID, i create a lamp and the appropriate power pole and the nerge them. Even added the traffic sign attached to the pole. Just be careful if you include the facing, use the <object>:direction key to indicate which one you are referring to.
Like @IanH says, you would be able to merge the features like explained here 
The problem with camera’s is the fact that both utility poles and surveillance features make use of the “man_made” key.
power=pole highway=street_lamp combine nicely. Combination used over 80 000 times, see highway=street_lamp | Tags | OpenStreetMap Taginfo
I think 5 separate nodes are already the best representation of this situation. Just add support=pole to each camera. That this refers to the closest pole is something an application can infer – one of the benefits of a spatial database.
I prefer the “one feature, one element” approach. Using the same node only kind of works if…
height, material, direction or operator which refer to only one of the merged objects.a simple tagging is just capacity=4 (or whichever amount of cameras) 
But then I can’t describe the fact that two of the camera’s are domes, two are ALPR’s, etc 
you can use the relation type=node for the cameras with an attached role where you put the pole node. It is a proposal and not widely used so far
Any conclusions here?
One node or three?
I’ll map three nodes for now.
you can use the node relation. 
https://wiki.openstreetmap.org/wiki/Proposal:Node
you can also map 3 unrelated cameras at the same spot.