Lucent Technologies AT&T 7400B - Manual (Page 111)

1. The voltage measured from Phase to Neutral should be 110 to 125 VAC.
2. The voltage measured from Phase to Ground should be 110 to 125 VAC.
3. The voltage measured from Neutral to Ground should be less than 1 VAC.
If the receptacle is not a properly grounded 3-prong type, stop the installation. Installation can
only be completed after a qualified electrician corrects the problem.