# = American Wire Gauge (AWG), the lower the number the larger the wire guage.
"Service cable" is large insulated stranded copper cable (usually refers to single #4 wire and up).
Most house hold circuits (Typically 15 - 30 amp) can safely handle 95% to 100% of it’s max rating - but only for an hour or so at a time. Loads that require long periods of 'on' time (like an air conditioner, ballasts, etc) should not exceed 80% to 85% of the max rated load of the wire/cable. The known safe capacity that the National Electric Code (NEC) recommends at 100%, is actually 80% of load.
99.9% of the time when you get into "insulated" #8 and bigger wire, it’s most likely going to be stranded (just like it’s big sister "Service cable"). You can usually get your basic sheathed xx/2 and xx/3 cable up to 6 guage. If you need larger than #8 or #6 though, you will have to buy service or "service type" cable. This can cause two problems. One: very high cost on long runs. Two: the cable might not fit the appropriately-sized breaker on a long run. This is why it’s wise to opt for putting your ballast on 240V when 2400+ watts of light power is needed on a single circuit.
#4 and above = Cable
1/0 and 2/0 are Service cable
120V (US) (@ 80% max load)
(50ft run or less)
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