breaker-boxcircuit breakersubpanel
I have a 240 volt 225 amp sub-panel. Both lines attached to the bus bar have 120v.
When I turn on any breaker connected to one of the bus bars, the voltage drops to 80-108v. If I remove the load and then turn on the breaker, I have 120v.
All breakers on the other bus bar when turned on do not affect the voltage. It remains at 120v.
Any idea what the issue is, as it doesn't seem to be the wire, the panel or the breakers.
Yes, you can add an insulated ground bar in the can (you should be able to get one specifically designed for your particular can, but here's what they look like):
.. and then connect it to the other ground bar using a piece of #4 AWG (solid bare copper, or stranded THHN insulated) assuming you're still at 200 amps. This guarantees that the green bonding screw that's actually bonding your neutral on the other bar will affect both bars if it is removed. It's common to add these for isolated grounds, where they're connected to a different ground altogether instead of the other bar.
Note - the one you buy may come with its own bonding screw, and the appropriate tapped hole to receive it - so check for that prior to connecting the two together (IOW, read the installation notes that came with it).
It sounds like you may be mistaken as to how this is wired, or that perhaps I'm just not understanding your explanation. As others have mentioned, it's not possible to get 240 volts from a single pole in a 120/240V split phase system. Each tandem breaker provides 2 120 V circuits, this is true. However, if you measure between the terminals on a single tandem breaker, you'll get 0 volts. This is because the terminals are both powered from the same leg, and so are at the same voltage potential. If you measure from a terminal on the top tandem breaker to a terminal on the bottom one, then you'll measure 240 volts. This is because each breaker is connected to a different leg, which are each one half of a 240 volt circuit.
With all that said. For this setup to work, one appliance would have to be connected to both breaker. Something like this...
Notice that each appliance circuit has one wire connected to each of the tandem breakers. In this situation, you'd need a device like Speedy Petey shows.
Which ties the breaker handles together, to provide common trip characteristics.
Notice how the inner handles are tied together, and that the outer handles are also tied to each other. This way if either trip (or are turned off by the user), the entire circuit is shut off.
If this is wired the way you've explained, where the dryer is connected to the top tandem and the heater is connected to the bottom. Then there's some magic going on in those breakers.
Best Answer
It sounds like a bad connection to the main breaker or a bad hammer in the main breaker. Try making the measurement at the main prior to the breaker. If your voltage is normal above the breaker the hammer in the breaker is not making a good contact. If it is the breaker turn your small breakers all off. With all the small breakers turned off flip the main breaker 10-20 times on and off and see if this cleans the contact. Sometimes this fixes the problem with a bad contact. but be prepared to replace the main if it happens again. If your voltage is low prior to the main you need to call the power company and have them check the connections at the transformer / line fuses on the pole for a loose connection. I just realized you said this was a sub panel if this is a sub measure the voltage coming out of the main and verify the breaker feeding the panel is not the problem other than that same procedure for checking the main in a sub. The next thing to try is swap L1 & L2 your 2 hots feeding the sub and see if the problem follows the wire.