I need to add a 50 amp circuit breaker in my Square D 150 AMP breaker box for the new hot tub. How do you determine if this will push the box capacity over the limit?

You have to do a load calculation. As a general statement, that is, you add up all of your maximum, known, simultaneous usage plus your general lighting (based on square footage of the house).

The other way is to put in the 50 amp circuit and wait to see if you have problems with overloading the main breaker. If you do you then have to heavy up or increase the size of your service.

So there is no danger in overloading the box, as it will simply trip the main breaker and you will then know you have to increase the size of the service?

Yes, if your total demand exceeds the 150 amps the main breaker will trip. Means you have to turn something off.

Yes, if your total demand exceeds the 150 amps the main breaker will trip. Means you have to turn something off.

Thanks Harold, I appreciate the advice.
:)

For most hot tubs we add a sub panel next to the original and use a specific GFCI made for tubs, about $90. HD and Menards carry them NEW Square D QO Hot Tub Pool Spa 50 Amp Breaker Panel - eBay (item 330363643114 end time Oct-04-09 21:07:58 PDT) (http://cgi.ebay.com/NEW-Square-D-QO-Hot-Tub-Pool-Spa-50-Amp-Breaker-Panel-_W0QQitemZ330363643114QQcmdZViewItem)

If you have electric heat, or large AC load, or other factors, a 200 amp service may not be large enough to handle a hot tub.