def current_ideal(P, V, phase=3, PF=1):
    """Returns the current drawn by a motor of power `P` operating at voltage
    `V`, with line AC of phase `phase` and power factor `PF` according to [1]_.

    Single-phase power:

    .. math::
        I = \\frac{P}{V \\cdot \\text{PF}}

    3-phase power:

    .. math::
        I = \\frac{P}{V \\cdot \\text{PF} \\sqrt{3}}


    Parameters
    ----------
    P : float
        Power, [W]
    V : float
        Voltage, [V]
    phase : int, optional
        Line AC phase, either 1 or 3
    PF : float, optional
        Power factor of motor

    Returns
    -------
    I : float
        Power drawn by motor, [A]

    Notes
    -----
    Does not include power used by the motor's fan, or startor, or internal
    losses. These are all significant.

    Examples
    --------
    >>> current_ideal(V=120, P=1E4, PF=1, phase=1)
    83.33333333333333

    References
    ----------
    .. [1] Electrical Construction, and Maintenance. "Calculating Single- and
       3-Phase Parameters." April 1, 2008.
       http://ecmweb.com/basics/calculating-single-and-3-phase-parameters.
    """
    if phase not in [1, 3]:
        raise Exception('Only 1 and 3 phase power supported')
    if phase == 3:
        return P / (V * 3 ** 0.5 * PF)
    else:
        return P / (V * PF)
