In 99 % of the cases red and red goes on one and black and black on the oth= er pole. If you want to make absolutely sure the primarys can be connected black to = black and red to red put the two reds on line of 110volt ac. Put one of the blacks on neutral (leave the secondary open for now) Measure voltage between the two blacks. if your voltage is near 0 volt ac p= olarity is correct and line belongs on the w=3Dtwo reds, neutral on the two blacks (or reverse= d) If=A0the voltage is near 220 volt one of the two coils needs to be reversed= . (black of one coil and red of the other on phase, and the other two on neutral.) Peter van Hoof ----- Original Message ---- > From: Harold Hallikainen > To: Microcontroller discussion list - Public. > Sent: Monday, July 13, 2009 6:15:09 PM > Subject: Re: [EE] Transformer wiring help > = > = > > I understand the center tap output with my choices for +12, -12=A0 or 24 > > VAC, Am thinking for 220 VAC, I want to connect the center red and black > > together, and the outer red and black go to the 220 VAC. For 110 volt, > > do I connect the reds together to say the hot 110, and the blacks > > together to the neutral 110? > = > Yes, that's right. For 240VAC, connect the two primaries in series. For > 120VAC, connect the two primaries in parallel. This is equivalent to a > single primary with double the wire size (cross-sectional area). > = > Harold > = > -- = > FCC Rules Updated Daily at http://www.hallikainen.com - Advertising > opportunities available! > -- = > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist = -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist