Cam Spider box

RJ Thomas

New Member
Hey Guys,
Have a question.

I have in the past used a cam spider box to combine services.


I just want to know the science behind it.


Also, if I combine a 200a and a 200a service will that be equivalent to a 400amp service on the other side?

Thanks,
 
Cam spider boxes aren't really combining separate services together, and no, you cannot combine 2 separate 200A drops together to make a 400A drop. This is for fundamentally the same reasons you can't do a reverse two-fer with dual 15A male connectors on it to make a 30A drop. Without getting too far into the mud on why that is, consider that 1) multiple power generating sources wouldn't like be shorted to each other, 2) if one input was turned off, the other input and everything upstream of it would be backfed and remain hot, and 3) you've compromised the ability for the overcurrent protection to behave as intended, by spreading a load out across multiple branches of circuit breakers and disconnects, making it unlikely for your overcurrent protection to keep you and your venue safe if something unexpected should happen, and 4) there are other reasons.

All those boxes are doing is giving you multiple inputs in parallel with one another, intended to be fed from a single, common source. So let's say you've got a generator kicking out 800A/leg. You need some heavy copper to run 800A, which at that point is basically copper bridge-suspension cable. Not really practical for someone to drag around unless they're dragging it with a truck. So they give you multiple taps off of the generator that you can run in parallel with common cabling solutions a mere mortal can handle. So you're not really combining 2 services of 400A together. You're loading an 800A power source across 2 sets of cables for 400A.
 
In simple terms, 4/0 cable is the most common feeder cable that is easily available, but is limited to a max of 400 amps. (Less in many applications.)
This simply lets you move more than 400 amps per leg from a source to a destination using commonly available cable.
 
There is no safe or legal way to parallel two of what I am assuming are company switches or something similar and not actual utility company services. Joining two breakers from the same distribution source back together again is not permitted for good reason. The only legal way to parallel breakers is to have them listed as an assembly by UL but at that point the NEC considers them as one breaker so the point is some what moot.
Paralleling separate sources is a different story. In the industrial arena paralleling generators, both temporary and permanent, is quite common. In a temporary setup a spider box could be used to join multiple generators but it would be a fraction of the equipment needed to make such a setup safe and legal. This should only be done by the rental company supplying the generator, attempting to parallel two generators with out understanding fully what needs to be done can result in the rapid unplanned disassembly of the generator.
 
Hey Guys,
Have a question.

I have in the past used a cam spider box to combine services.


I just want to know the science behind it.


Also, if I combine a 200a and a 200a service will that be equivalent to a 400amp service on the other side?

Thanks,

There is no science behind it; it's dangerous and absolutely violates Code.

DO NOT DO THIS.
 
I get presented with this situation (minus the spiderbox) often at convention centers. The easy answer is to bring 2x dimmers or distros, and feed them each 200 amps. Combining them, as stated above, is only going to bring you trouble.

Yeah like 300A trying to go down cabling to a service thats meant for 200A.... Joining two 200A sets of cable not not mean that 200A with go down each when loaded to 400A. Chances are all 400A will attempt to go down ONE set.
This is a complicated issue that requires a lot of electrical engineering knowledge.

Simply... Oh you have two 200A services? Well you have to use them as two 200A services. Honestly that should be quite sufficient, just divide equipment accordingly to each one. And please try and balance loads.
 
I made a disto box that drops between the power source ( genertor or house power) that has multiple outlets. (6) 60 amp 3ph, (6) 20 amp 3ph (6) 50 and single ph (3) cam out. With this set up I can handle individual spide box's or "lunch box style disto 60 amp 3ph ea." convention stringers, and more can out to additional carnival style outlets, or more 50 amp single ph, socopex, 400A 3 Phase Motion Picture Box, etc, total can handle 1,200 amps out in any set of combinations all digattly metered so I can see how much otput is going to each leg and adjust accordingly. After years of fighting disto's and power I made this beauty to handle anything that I can throw at it in any type of configurtaions.
 
There are large boxes meant for combining the outputs of 2 or more generators together, the generators run synchronized, share the load, and create redundancy that eliminates the need to power down and manually switch over to another source, provided that one generator has the capacity to supply the entire load.
 

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