Is it only one breaker that's tripping? If so, what current is the
breaker that's tripping rated for? If it's 15A or even 20A it may
just be doing it's job, as A/C's can draw a lot of current, and 3
running off a single line could be drawing significant current when
all the compressors switch on, etc... which may be why it takes a
minute, just until they are all drawing maximum current. Check each
A/C unit for it's current rating, if any, on the label. Add them up,
and if the wire, lines, plugs, and breaker are all rated for the
current, but it still blows, it could be a bad breaker, they do get
old and sometimes just trip under less of a load then they're rated
for. If you're experienced in electricity delivery you could try
changing the breaker with an exact replacement, but of course there's
240VAC (usually) present at the breaker box at all times, even when
the main breaker is shut off (the delivery to the main breaker stays
on constantly), so be careful or you could get fried. Best to have an
electrician come and check it if you're at all uncomfortable with
doing it yourself. You could just test the line coming out of the
breaker with a clamp on type current meter if you have one (you have
to take off the front breaker panel, usually four large flat headed
screws) before you try changing the breaker just to check out the
current draw. Either way, be careful, all it takes is a slip of the
screwdriver to hit one of the distribution blocks which aren't
insulated and have lethal potential.
