Critical questions about workshop wiring
Adequate electrical service
A: Look at the number printed on the main breaker in your service panel determine the total amperage available to your home from the power supply line. This tells you the maximum amperage that all electrical circuits can draw simultaneously. Most homes built in the past 40 years are equipped with 100- or 200-amp service, which should provide ample power to run your household and, in many cases, a shop. Plus, the service panel may have unused circuits available for your shop wiring needs.
Even if you have space for extra circuits, consider running a separate feeder to a subpanel in your shop. Advantages include nothaving to share circuits with the house, snaking just one large cable instead of multiple smaller ones, and being able to shut off shop power when it's not in use.
Adding a subpanel also allows shorter wiring runs in the shop, which decrease power loss and heat buildup. But, a subpanel won't increase your total capacity. In other words, if you have 200-amp service, and you split off 80 amps to a subpanel, you don't have 280 amps available.
If your home was built before the 1950s and hasn't been electrically updated, you may have only 60-amp service. If that's the case, if you still have a fuse box, or if you frequently trip breakers, you need increased service and a new panel.
Be aware, too, that if your shop is located in a garage or unfinished basement, electrical codes will likely require Ground-Fault Circuit Interrupter (GFCI) protection on all general-use outlets. These devices detect current leaks and shut down power instantly if a short occurs. GFCI outlets protect specific areas within a circuit, while a GFCI breaker serves the entire circuit.
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