Can I tie the neutral and ground together?

Neutral wires are hazardous-live-parts; that is, they are normally current-carrying conductors that carry the same amount of electrical current as our hot wires. Within our electrical codes, neutral wires are treated exactly the same as hot wires: they are insulated and made inaccessible to people. Ground (or Protective Earth) wires are normally non-current-carrying conductors and are designed to be the low-impedance, fault-current path during accidental fault conditions. Within our electrical codes, ground wires are treated the same as all other exposed touchable metallic objects. Ground wires are often not insulated (bare) and are accessible to people. NEC Article 250.24(B) NEC Article 250.28 NEC Articles 250.6(B) 250.24(A)(5) HB Notes 250.30 HB Notes “Application Examples 1, 2 and 3” 250.30(A) 250.30(A) HB Notes “Common Misconception” 250.30(A)(1) 250.30(A)(1) Exception #2 250.30(A)(1) Exception #3 (a) and (b) 250.30(A)(5) HB notes 250.32(B)(1) HB notes 250.142(B) HB Exhibit 250.8 If your electrical panel is a subpanel, then NO, you do not make a neutral-to-ground connection. You should have an equipment grounding conductor routed to your sub-panel that is in compliance with NEC Table 250.122. If your electrical panel is the first service disconnect point, AND the utility has only provided normally current-carrying conductors (phase and neutral wires), then YES, you must make a neutral-to-ground connection (i.e., 3-phase/4-wire or 1-phase/3-wire). If your electrical panel is the first service disconnect point, and the utility has only provided normally current-carrying conductors (phase and neutral wires) PLUS a ground wire, then NO, you do not make a neutral-to-ground connection (i.e., 3-phase/5-wire or 1-phase/4-wire). A high-resistance reading (typically greater than 200 ohms) indicates that there are no metallic paths between the panel and the transformer, and therefore a neutral-to-ground bond in a grounded system is required. A low-resistance reading (less than 1 ohm) indicates that a continuous metallic path does exist, and that a neutral-to-ground bond should NOT be installed. You should also go back and install a ground wire (5-wire system) between the source transformer and the panel. Unfortunately, the NEC does not tell us what to do when the measured resistance between the panel and the transformer chassis is between 1 and 200 ohms. However, the IEC does provide guidance in this scenario (for our IEC clients, this is the classic TT vs. TN-C-S vs. TN-S systems debate). E&S would recommend that you convert your 3-phase/4-wire or 1-phase/3-wire to a 3-phase/5-wire or 1-phase/4-wire system by pulling a ground wire from the transformer to the main panel and removing any neutral-to-ground bonds in the panel. Note: The reason for this is because the soil resistivity of the earth itself can be so conductive that it can act as a conductor enabling neutral currents to travel through the earth back to the transformer during normal operating conditions.