Installation manual

McQuay IM 487-4 49
Electrical Installation
All Units
The minimum circuit ampacity (wire sizing amps) is shown on
the unit nameplate. Refer to Table 13 on page 49 for the
recommended number of power wires.
Copper wire is required for all conductors. Size wires in
accordance with the ampacity tables in Article 310 of the
National Electrical Code. If long wires are required, it may be
necessary to increase the wire size to prevent excessive voltage
drop. Wires should be sized for a maximum of 3% voltage
drop. Supply voltage must not vary by more than 10% of
nameplate. Phase voltage imbalance must not exceed 2%.
(Calculate the average voltage of the three legs. The leg with
voltage deviating the farthest from the average value must not
be more than 2% away.) Contact the local power company for
correction of improper voltage or phase imbalance.
• A ground lug is provided in the control panel for each
disconnect or power block. Size grounding conductor in
accordance with Table 250-95 of the National Electrical
Code.
• In compliance with the National Electrical Code, an
electrically isolated 115V circuit is provided in the unit to
supply the factory mounted service receptacle outlet and
optional unit lights. This circuit is powered by a field
connected 15A, 115V power supply. Leads are brought in
through a 7/8" knockout in the bottom of the main control
panel, near the power wire entry point.
1.All wire sizes assume separate conduit for each set of parallel conductors.
2.All wire sizes based on NEC Table 310-16 for 75°C THW wire (copper).
Canadian electrical code wire ampacities may vary.
3.All wire sizes assume no voltage drop for short power leads.
CAUTION
Provide proper line voltage and phase balance.
Improper line voltage or excessive phase imbalance constitutes
product abuse. It can cause severe damage to the unit's
electrical components.
Table 12: Multiple point power connection options
Number of
electrical
circuits
Disconnect
designation
Load
Location
(see Figure 8 on
page 8)
2 DS2 Supply and return fan
motors plus controls
Main control panel
DS1 Balance of unit Main control panel
2 DS3 Electric heat Electric heat
control panel
DS1 Balance of unit Main control panel
Table 13: Recommended 3-phase power wiring to ensure
disconnects and power blocks mate with power wiring
Wire
gauge
Qty./
pole
Insulation
rating
(°C)
No. of
conduits
Conduit
(trade size, in.)
For MCA
up to
(amps)
10 1 75 1 1/2 35
8 1 75 1 3/4 50
61 75 1 1 65
41 75 1 1 1/4 85
3 1 75 1 1 1/4 100
2 1 75 1 1 1/4 115
1 1 75 1 1 1/4 130
1/0 1 75 1 1 1/2 150
2/0 1 75 1 2 175
3/0 1 75 1 2 200
4/0 1 75 1 2 230
250 1 75 1 2 1/2 255
300 1 75 1 2 1/2 285
350 1 75 1 3 310
400 1 75 1 3 335
500 1 75 1 3 380
3/0 2 75 2 2 400
4/0 2 75 2 2 460
250 2 75 2 2 1/2 510
300 2 75 2 2 1/2 570
350 2 75 2 3 620
400 2 75 2 3 670
500 2 75 2 3 760
250 3 75 3 2 1/2 765
300 3 75 3 2 1/2 855
350 3 75 3 3 930