Hi Tom Poe,

The calculation is pretty straight forward

When you have 110V mains and the fuses are for example 16 amp than you can draw 110Vx16A=1750Watt from one Fuse, for 220V it is just double about 3500W

Your shop lights will draw about 45 to 50W each tube so 12x50=600W total

You have about 1750-600 or 3500-600 Watt for you heat pads

When you have heavier or lighter fuses just redo the calculation

Sorry, scorpio-bafh, but it is more complicated than that. See

https://en.wikipedia.org/wiki/Power_factor

Using the symbols given,

A = P/((power factor)*V)

The heating pad is a resistive load therefore power factor = 1 and your calculation is correct but for the shop lights, 0 < power factor < 1, so the current will be greater than you predicted.

"do I need to worry about blowing fuses? Can anyone help point me to learn how I might calculate power use for my setup?"

You need to know the total current, not the power, to select the proper fuse. The easiest way to determine the total current is to use a Kill A Watt meter that can be bought for about $20 at Menards or Home Depot.

Tom - What is the voltage where you are located? You will need a bit more information to do the calculation.

Here is a calculation method for flourescent light power consumption:

• 54W bulb rating (written on side).
• 6x T5HO bulbs.
• 6x 54W = 324W
• 324W / 120V = 4.5A
• 4.5A * 1.1 * 1.1 = 5.4A (Most ballasts are 90% efficient, >0.9 PF).

Here is a calculation method for heat mat power consumption:

• 60W heat mat rating (product description).
• 2x heat mats.
• 2x 60W = 120W
• 120W / 120V = 1A
• 1A * 1.2 = 1.2A (Most AC/DC adapters are >80% efficient, 1.0 PF).

Then add both:

• 5.4A + 1.2A = 6.6A total amps.
• If you are using old ballasts or heat mats, consider adding 20% margin on top of this to be conservative.

If you are in North America, receptacle circuits are typically rated for 15A.

• You can check your breaker or fuse panel for the circuit rating.
• 15A * 0.8 = 12A max continuous rating (home breakers are rated for 80% continuous duty)
• 6.6A < 12A, therefore the circuit should be okay.
• Don't forget a single circuit powers many receptacles and often lights. So your lights+heat mats may not be the only load.
• The 80% continuous rating is important because if you exceed it, everything will work fine until the thermal-magnetic element heats up and trips. If not corrected, you will eventually need to replace the breaker.

To determine the load of your grow setup, you can use a plug-in power meter (such as a Kill-A-Watt). Often you can borrow them free from local libraries.

If you want to know the actual load on a breaker you will need a clamp-on power meter. They are quite expensive.