We still must address the issues of heat dissipation, working clearance, and nearby combustible materials. So, do we have the proper location for our transformer? Well, not yet. A transformer not in excess of 50 KVA may be located in a hollow space of a building-such as in a suspended ceiling-and does not require ready access. A transformer that is 1,000 V nominal or less may be located on walls, columns, or structures in the open and does not require ready access. However, some significant additional permissions to this rule exist.
Is the transformer readily accessible as required by NEC Section 450.13? The general rule of this section is that the transformer must be readily accessible. Where do we go for these requirements? Let’s start with 2017 National Electrical Code ( NEC) Article 450. The dry-type grounded transformer at or under 112.5 KVA with the system bonding jumper installed in the transformer enclosure that we are addressing in this article must be placed in a location that provides working clearance, safe distances from combustible materials, ready access, and proper heat dissipation. Let’s look at the basics of a grounded 480/277 V to 208/120 V wye-type transformer supplying a panelboard in a typical retail or office space.
Electricians and Inspectors who feel very confident with installing and inspecting electrical services will sometimes be far less comfortable when dealing with grounded-type transformers installed on the load side of a building’s service disconnecting means.
Many field electricians, design professionals, and inspectors struggle with these installation requirements. The most routinely encountered transformer installation is likely the common three-phase 480/277 volts (V) to 208/120 V wye dry-type transformer supplying a panelboard.
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